The leader of Caerphilly council has dramatically resigned from the Labour Party, calling it a “busted flush”.

Sean Morgan’s decision to quit the party means he has left his job as leader, and comes days after Labour launched it’s Caerphilly Senedd by-election campaign.

He said he would be voting for Plaid Cymru, and he attacked Labour for selecting an “unknown” to stand.

Morgan alleged there had been a “fix” for the party’s Caerphilly selection because his deputy leader was unable to stand – Labour said it applied “robust due diligence”.

The council is to begin the process of electing a new leader. Labour, which has a majority on the council, retains control of the authority. Morgan remains an independent councillor.

A Labour source said Sean Morgan had been unhappy with the party for some time.

The Senedd by-election comes after the sudden death in August of Labour Caerphilly Member of the Senedd (MS) Hefin David.

Morgan said his “moral standing does not allow me to be aligned with the Labour party any longer”.

Morgan told BBC Wales: “I’ve been unhappy with Keir Starmer and the leadership generally.

“Keir Starmer seems to have done none of the things he promised and all of the things that he never mentioned.”

He called the UK government “complicit” with Israel’s actions in Gaza, and criticised how Labour handled the selection for the Caerphilly seat.

Labour announced that children’s book publisher Richard Tunnicliffe would stand at the weekend.

Tunnicliffe has been campaigns and canvassing officer for the Caerphilly Labour Party, and has said he had been working with Hefin David on standing for election.

Morgan accused Labour of having “twisted the rules” to disallow some members – including deputy Caerphilly council leader Jamie Pritchard.

“They have not allowed members to have their say on who they want,” said Morgan.

“So we have now had a Johnny-come-lately candidate that is pretty much unknown within the Labour Party in Caerphilly, and we are now told that we must go out and support him.

“It just came home to me that the Labour Party is very simply a busted flush and I can no longer be a supporter of it.”

In a separate interview with the Local Democracy Reporting Service (LDRS), Morgan said Pritchard failed the initial screening for would-be candidates, for a variety of reasons ranging from tweets in support of then-UK Labour leader Jeremy Corbyn to newspaper coverage of his council duties.

Morgan alleged the justifications for barring “hardest-working” councillor Pritchard amounted to “absolutely nothing of significance”.

Councillor Morgan said another potential candidate, Chris Carter, was allowed to be put forward in apparent conflict with party rules, which had barred those already selected elsewhere for the May 2026 election from standing.

He alleged that Welsh Labour secretary Joe Lock had changed selection rules the night before a hustings took place last Saturday.

“Joe Lock, who clearly thinks he’s Malcolm Tucker from The Thick of It, said the rules had been changed the previous night and that was the way they were running it – there was no discussion,” he said.

Labour denied that any changes were made to the process – and said Richard Tunnicliffe has been a member of the Labour Party since he was 15 and has lived in Caerphilly since 1999.

Morgan told LDRS that he will “be voting for Lindsay Whittle” – the Plaid Cymru candidate and former council leader.

“Lindsay Whittle was chosen by 200 members of his party, in an election that I understand was run in a fair manner.

“He is a man of the people – he has always worked for the people of Caerphilly.”

A Welsh Labour spokesman said: “We can confirm that councillor Sean Morgan is no longer a member of the Labour Party. He has given his reasons.

“His former council colleagues, and we as a party, are focused on delivering for the people of Caerphilly.”

In response to the allegations about the selection process, the spokesperson added: “This is a by-election that none of us wanted to face.

“While we do not comment on the selection process for individuals, we have robust due diligence processes in place agreed by the Welsh Executive Committee to ensure everyone selected to stand for the Labour Party is shares the party’s values.”

A Plaid Cymru spokesperson said: “In this by-election, we encourage people to put their trust in Lindsay to send Labour a clear message in Cardiff and London that Caerphilly – and Wales – won’t be ignored any longer.”

Reform is expected to announce its candidate this week.

A Reform UK Wales spokesman said: “Welsh Labour are in chaos. Both they and Plaid have failed local communities in Caerphilly and Wales, so it’s no wonder that Morgan has resigned instead of defending their disastrous record.”

The Conservatives have picked Gareth Potter to stand in the by-election.

A Conservative spokesman said: “The Welsh Labour Party is in complete turmoil, locally in Caerphilly, and right across Wales.”

Independent Blackwood councillor Nigel Dix said: “The timing of this announcement is designed to do as much damage to Labour as possible in the coming by-election.

“I think the Labour party is in turmoil regionally in Wales, nationally in Westminster and locally in Caerphilly. They are putting their own party political squabbles above the needs of the people.”

The Caerphilly by-election is due to take place on 23 October.