Image source, Matthew Horwood

We have come to the end of our live coverage, but let's recap on what's happened over the past 14 hours.

• It was an historical evening as Plaid Cymru's Lindsay Whittle won the Caerphilly by-election, taking the seat from Labour.
• The party's leader Rhun ap Iorwerth says the victory is "a reset for Welsh politics".
• Welsh First Minister Eluned Morgan admits this was a "bad result for Labour", who came in third behind Reform UK, but says she will not resign.
• Reform candidate Llyr Powell says he's confident his party will win enough seats in May's election and party leader Nigel Farage adds that it'll be a "two-horse race between Reform and Plaid Cymru".
• It was an exciting evening for Caerphilly, but it's only the start as political parties gear up for next year's Senedd election.

To read more about last night's event, click here.

Vaughan Roderick
BBC Welsh affairs editor

If you look at the history of Caerphilly, you have got to go back over a century to the 1920s to see a result anything like this.

Plaid Cymru did come close to taking the Westminster seat way back in 1968. They won the constituency on the list vote in 1999, but nothing like this sort of collapse in the Labour vote.

This is a vote against 28 years of Welsh Labour government in Cardiff Bay, but it's also a vote against Keir Starmer's track record in Westminster, in particular in fact, his attempt to move the party to the right to try and out Reform, as some people put it.

From word of mouth, it appears what has happened in Caerphilly is there was a very strong and unexpectedly strong turnout from younger voters.

What do we know about younger voters in Wales? Well, they are the cohort that are most in favour of Welsh Independence, the cohort who are the most opposed to Brexit, and they are the cohort who are the least likely to vote for Reform.

If we see an electorate that reflects that next May, then that's very bad news for Labour, bad news for Reform and the Conservatives, and it's very good news not just for Plaid Cymru, but also for the Green Party and the possible new Jeremy Corbyn party.

Paul Pigott
BBC News

The Police's "Every Breath You Take" was top of the pops the week Lindsay Whittle first campaigned to become a Plaid Cymru MP. He won 6,414 votes on 9 June 1983 in his first of 13 failed attempts to be elected to both Westminster and Cardiff Bay.

Born in Caerphilly town, Whittle lives in Abertridwr, was raised on the Penyrheol council estate and attended Cwm Ifor Primary School.

A councillor for Penyrheol since 1976, he was Caerphilly council leader from 1999 to 2004 and 2008 to 2011, and has been Plaid Cymru group leader on the council since 2022.

From 2011 to 2016 he was a South Wales East assembly member, as Senedd members were previously known.

Whittle was replaced in 2016 by Plaid's Steffan Lewis.

Image source, PA Media

After so many disappointing election counts in Caerphilly, Whittle began his acceptance speech after finally winning with a joke.

“I’m not used to speaking first in these election counts," he said, drawing laughter then applause from the crowd.

Lindsay Whittle has now been sworn in.

He is now the Senedd member for the Caerphilly constituency.

It's been a long night for our political reporters who have brought reaction and analysis to Plaid Cymru's victory overnight across BBC Wales' live stream coverage.

Straight off the back of the result, BBC Wales' political experts Gareth Lewis, James Williams, Teleri Glyn Jones, and Felicity Evans joined forces to debrief in a new Walescast episode: The Morning After The Night Before.

They discuss the winners and losers and what it could all mean for the Senedd election in May.

Lindsay Whittle will shortly be sworn in as Caerphilly's new seat holder, for the very first time.

It will mark the end of 100 years of Labour holding their seat in Caerphilly.

Image source, Matthew Horwood

Image source, PA Media

The UK government said it understands people are "disappointed" with the pace of change, but it is determined to go "further and faster" in delivery, after Labour's by-election loss in the Welsh Parliament.

In a statement, the press secretary of Prime Minister Sir Keir Starmer said: "By-elections are always difficult for incumbent governments.

"This one is no different, but we are determined to show the people of Caerphilly and working people across Wales the change the UK Government is delivering hand in hand with the Labour government in Wales.

"[We are] determined to go further and faster, understand people are disappointed with the pace of change, and that is what the government is relentlessly focused on delivering for working people in Wales and across the UK."

The turnout for the by-election was just over 50% - higher than 2021's 44% in Caerphilly.

The national average for a Senedd vote has never been over 50%.

Reform won only 495 votes four years ago but ended in a two horse race with Plaid Cymru in Thursday's poll, coming second with 36% of the vote.

Despite the result Reform candidate Llŷr Powell said he thought Reform will form the next Welsh government.

There are no prizes for coming second in first-past-the-post, but capturing 36% of the vote after winning just 2% in 2021 is no mean feat.

Reform UK is developing an increasingly sophisticated campaign machine and will have learned from this experience.

Figures in the party say they still expect to win the coming Senedd election.

What does Caerphilly mean for the Senedd election?

The record turnout of 50.43% suggests that, when you introduce some jeopardy into the mix, voters do become engaged.

The message of change, mixed with some voters being motivated to back Plaid to stop Reform, proved the winning formula for Plaid Cymru this time.

Read more here

Image source, PA Media

As eyes turn to the full Senedd election in May, last night's result raises some key questions about what is clearly now a very different political world in Wales.

How did Plaid Cymru pull it off?

Plaid Cymru successfully presented itself as the vehicle for change from a deeply unpopular Labour UK government and a Welsh Labour party that's been ruling the roost since Tony Blair's landslide victory in 1997.

Aided by opinion polling showing Labour on the slide and Reform on the rise, Plaid Cymru was able to frame the by-election as straight choice between itself and Nigel Farage's party.

Where does Labour go from here?

A Labour loss was widely expected, so a victory for the party would have been astonishing, but that does not diminish the significance or nature of this defeat.

There are, naturally, caveats. By-elections are frequently different beasts from full elections, Caerphilly voters might behave differently in just a few short months.

But this close to that full Senedd election, Labour appear to be in deep in the mire.

Image source, Reuters

Andrew RT Davies, former leader of the Welsh Conservatives, says Plaid Cymru's victory in the Caerphilly by-election should be a "wake-up call" for unionists.

Mr Davies says: "Separatism is corrosive, with the aim breaking apart our nation and no regard to its consequences on the living standards of the people of Wales.

"Plaid have escaped the scrutiny subjected to other parties for too long, portraying themselves as a harmless protest vote while they pursue their extreme ideology.

"The separatists' victory in Caerphilly must be a wake-up call and the onus is on those of us who believe in the Union to show the people of Wales the real Plaid."

As Plaid lap up with victory parade; they sense political change on the cardspublished at 12:19 BST

12:19 BST

Tomos Morgan
Reporting from Caerphilly

Image source, PA Media

We have had the victory parade here in Caerphilly where Lindsay Whittle and Rhun ap Iorwerth lapped it up.

They enjoyed this moment because they sense a big opportunity not only due to this win but also looking ahead to the Senedd elections next year.

Ap Iorwerth has said this morning he believes huge new political change is on the cards here in Wales. Labour have been a dominant party here for decades - a century in Westminster - but things have now changed.

I have been speaking to some people to find out why there has been such a shift; some tell me it is the way Welsh Labour have been performing in the Senedd and not being happy with their results on the NHS.

Some are not happy with Sir Keir Starmer and some are not happy with the Labour-run council in Caerphilly and their decision to try to cut libraries and other public services due to other budget cuts.

What I think is really interesting is the high voter turnout, 50%, and that demographic.

The question for Plaid will be can they continue this momentum, while questions for Labour will be how do they rebuild in the Senedd, in Westminster and locally as well.

Following on from Nigel Farage's remarks, a spokesperson for Reform UK in Wales says the Labour party is "finished" in the nation and likened the Conservatives as going "the way of the dodo".

“This is a historic realignment in Welsh politics," the spokesman says.

“Next year, the choice before the Welsh people will be between open borders madness with Plaid Cymru, or common sense with Reform.

“We are fighting to win the next election, to enter Welsh government, and to ensure that our left behind communities will be left behind no longer.”

Image source, PA Media

Reform UK leader Nigel Farage has given his reaction to the Caerphilly by-election result - after his party's candidate came second.

"At the start of polling day, I thought that we would get 12,000 votes and we did," Farage writes on social media.

"I thought that number would be enough, but it wasn’t.

"The total collapse of the Labour vote to Plaid was to a party that people know well and to a popular local politician.

"The Senedd elections next year are a two-horse race between Reform UK and Plaid Cymru."

Image source, Reuters

Labour's First Minister of Wales, Eluned Morgan, says Prime Minister Keir Starmer understands "that he also has a responsibility to help us out in Wales", following their defeat in the Caerphilly by-election.

She admitted that this was a "bad result for Labour" and that there are "serious lessons for us to learn here at all levels of government".

But she insisted that she would not be resigning, adding: "I've got too much work to do."

In an interview with BBC Wales, Morgan said she spoke to Starmer on Friday morning, and said that she will be asking for more from his government.

She said the Welsh government were delivering on people's priorities but accepted that they had more work to do.

"We're taking this extremely seriously. It is important that we listen to the public," she said.

Despite only winning 11% of the vote, Morgan said they had difficult elections before and had "bounced back"

Looking ahead to the Senedd election in May she said: "All is not lost, I think its really important that we learn the lessons."

Jordan Davies
BBC News

At Caerphilly castle, Plaid Cymru supporters are continuing their celebrations following the party's victory in the by-election.

Lynne Hughes, 59, a Plaid community councillor for the Van ward, described Whittle as being an " amazing activist in Caerphilly for so many years".

"On an individual level, [I'm] delighted for him, delighted for Plaid in terms of what this means, hopefully, in terms of the Welsh election in May,  and also absolutely delighted that the people of Caerphilly have rejected Reform."

Jeff Grenfell, 53, Plaid councillor for the Twyn ward, says today has been a "long time coming" and that he is "absolutely delighted" with the results.

"I think it proves to people that they can vote for Plaid Cymru and Plaid Cymru can win."

"And also it hopefully brings the idea of eventual independence for Wales more to the forefront of daily political discussions, and to prove that is a thing that ultimately will be better for people's lives everywhere in Wales."

Plaid Cymru's headline policies are set out to stand for "fairness, ambition, and Wales".

These include:

• Securing £4bn "owed to Wales" from the HS2 project to invest in improving public transport in all parts of the country and reversing cuts to local bus services.
• Fair funding from Westminster to invest in the NHS workforce and recruit 500 GPs into Wales, as well as a new cancer strategy to ensure cancers are caught and treated earlier.
• Help 330,000 Welsh families to deal with the cost of living crisis by increasing child benefit by £20 per week.
• Redressing economic unfairness by increasing windfall taxes and devolving the Crown Estate

Charlie Buckland
BBC Wales

Rhun ap Iorwerth, 53, was born in Tonteg, near Pontypridd, in south-east Wales, but grew up in the north west of the country - spending his first few years in Meirionnydd before moving to the island of Anglesey, aged five.

His father was a teacher and prominent singer, composer and campaigner for the Welsh language and culture, while his mother, also a teacher, was president of a number of bodies promoting Welsh.

He spent about two decades as a high-profile political journalist reporting for BBC Wales before leaving the broadcaster in 2013 and securing the Senedd seat of Ynys Môn for Plaid Cymru.

Ten years on, the father-of-three was elected unopposed as the party's leader in 2023, after the dramatic resignation of Adam Price.

Since taking over as leader, ap Iorwerth has assumed a more confrontational approach to the Labour government in the Welsh Parliament, including ending Plaid's co-operation agreement with Labour ministers that his predecessor, Price had signed.

In July 2024, Plaid Cymru secured its best-ever result at a UK general election winning four Westminster seats - but it has never won a Senedd election since devolution in 1999.

Nicky Campbell has been speaking to 5Live listeners about the by-election results.

Alun, from Caerphilly, says it had been “quite an intense and sometimes febrile campaign”.

“What Hefin [David] was about was bridge building between different elements of the community. We’re in danger of losing that bridge building and developing some kind of tribal bonding”.

Rob in Caerphilly says he is “happy” with the outcome.

“I was thinking about moving, my bags were already packed. I thought Reform we’re gonna get it," he said.

Darren, from Caerphilly, said he is happy that "decent, hardworking politician has won" and that constituency winner Lindsay Whittle is "a man of the people".

“Reform did well because people want change, Labour have become stagnant and Plaid are offering a change to the left, Reform are offering a change to the right," he said.

Amelia Shone-Adams
BBC News

Our reporter has been speaking to Freya Jenkins, 19, a university student in Cardiff who is from Caerphilly.

She says she has been "very worried" in the run up to the election, and believes Reform stands for the "complete oppsite of what Wales stands for".

In terms of Labour losing their seat, Freya, who studies Welsh,  says she thinks it's something that was needed and that "it's time for a change".

Freya would like to see Rhun ap Iorwerth as first minister after next year's election and she thinks it's time that "Wales starts standing up for itself".

"I would think it's really important that we start prioritising us, we start prioritising our language and we start prioritising keeping our traditions and our heritage," she said.