Keir Starmer was under intense pressure on Friday night after Labour’s crushing by-election defeat in a seat it had held for 100 years.

The Prime Minister’s leadership was called into question after the disastrous result in Caerphilly, South Wales.

There was some consolation for Labour as Reform UK was pushed into second place despite leader Nigel Farage having pledged to ‘throw everything’ at winning, with Plaid Cymru romping home in the race for the Welsh Senedd.

The result raises the prospect of Labour losing its power bases in Wales and Scotland at local elections in May next year.

Polling expert Professor John Curtice said the party is in ‘severe trouble’ in Wales, with polls suggesting it could lose its first minister for the first time since devolution.

He said Plaid Cymru are ‘well placed’ to provide the country’s next leader, but told the BBC the result does ‘not suggest that Mr Farage’s bubble is burst’.

Plaid’s Lindsay Whittle got 47 per cent of the vote, Reform’s Llyr Powell got 36 per cent with Labour’s Richard Tunnicliffe on 11 per cent – a collapse of 35 per cent on 2021.

The Tories won just 2 per cent of the vote, their worst by-election result in history, while the swing from Labour was almost 27 per cent on a high turnout of more than 50 per cent.

Following the election, triggered by the death of previous incumbent Hefin David, Labour MPs said the party risked losing support on its Left and Right flanks.

Caerphilly MP Chris Evans said ‘lessons must be learned’, while Mainstream, a group linked to Sir Keir’s potential leadership rival Andy Burnham, said the party was ‘detached from its moral purpose’.

Labour’s First Minister in Wales, Baroness Morgan of Ely, said the vote came ‘in the midst of difficult headwinds nationally’.

Senior sources told The Times the PM was now ‘in a dangerous position’.

Sir Keir said he was ‘deeply disappointed’ and that ‘we clearly need to do much more’.