Liberal Democrat Rhys Taylor in Cardiff North has become the second of his party’s general election candidates to advise supporters to vote tactically for their Labour rival to defeat Conservatives.

Mr Taylor followed Brendan Devlin in Stockton South, who this morning effectively endorsed his Labour rival in a key marginal seat in the North-East.

At this late stage in the campaign, it is not possible for candidates’ names to be removed from the ballot paper or for voters to be stopped from marking their X by their names. But it is thought that advice from candidates to vote tactically could produce a potentially decisive shift in votes.

Cardiff North was taken by Labour’s Anna McMorrin by a margin of eight points in 2017 after being in Tory hands since 2010.

Last night’s MRP polling analysis by YouGov suggested that Ms McMorrin was on course to retain the seat, with a 53 per cent vote share putting her comfortably ahead of her Conservative rival on 33 and Mr Taylor trailing a distant third on five per cent.

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But the Lib Dem’s decision to speak out may influence supporters of third-placed parties elsewhere in the country to switch in favour of the referendum-backing candidate most likely to beat the Conservative.

In a message to voters on Twitter, Mr Taylor said: “You have a decision to make in Cardiff North tomorrow.

“I’m standing to give voters dismayed by the big two a chance to vote Liberal Democrat. But if you want to deny Johnson and the Conservatives a majority, vote tactical not tribal.”

Earlier, Mr Devlin issued a string of tweets saying that while he could not endorse Jeremy Corbyn or the Labour Party nationally, he regarded the party’s candidate in Stockton South Paul Williams as “an honest, sincere man”.

Acknowledging the seat was “a Lab/Con battle”, he urged his supporters to “vote tactically for someone who cares about the NHS and social care” - effectively pointing them to put their cross next to Dr Williams’ name.

Their moves came after campaigners for a Final Say referendum on Brexit issued a call for Liberal Democrat and Labour candidates in 20 key general election seats to cease campaigning and announce they are voting for Remain-backing rivals who stand a better chance of denying Boris Johnson a majority.

Mr Devlin was top of the Vote for a Final Say (VFS) list, as polls suggested his small band of supporters could make the difference between Labour or Conservatives seizing the seat.

Polling by Survation suggested that Tory Matt Vickers is currently on course to win the North-East England seat by a margin of 46 per cent to 43 per cent, with Mr Devlin trailing in fourth, behind the Brexit Party, on just 3.4 per cent. But the poll suggests that if the Lib Dem candidate urged supporters to back Dr Williams, he could hold the seat by a margin of 48-43.

Liberal Democrats have stood aside for Green and Plaid Cymru candidates as part of the Unite to Remain alliance, and are not putting up candidates against former Tory europhiles Dominic Grieve and Anna Soubry. But leader Jo Swinson has set her face firmly against any deal with Jeremy Corbyn’s Labour.

VFS is calling on 14 more Lib Dem candidates and five from Labour to “get out of the way” of the drive to block a hard Brexit by halting their campaigns and urging supporters to vote for rivals who are better placed to defeat Tories.

Among seats on the list were Liberal Democrat targets Cheadle, Cheltenham, Winchester, South Cambridgeshire and St Albans, where Jo Swinson’s party could be assured of victory if Labour voters threw their ballots behind the Lib Dem candidate.

Constituencies where the group recommended Lib Dem candidates to stand aside included Brexit figurehead Iain Duncan Smith’s Chingford and Woodford Green, where the former Tory leader is believed to be vulnerable to a challenge from Faiza Shaheen, and Putney, where Labour are hoping to snatch the onetime seat of ex-minister Justine Greening.

Elsewhere, VFS are urging Lib Dem candidates to stand aside in constituencies won by Labour in 2017 where Mr Corbyn’s party are hoping to avoid losses to Tories.

They include Canterbury, where original Lib Dem choice Tim Walker stood down in favour of Labour’s pro-referendum Rosie Duffield, only for Ms Swinson to impose another candidate.

Mr Walker said: “I beg other Lib Dem and Labour candidates in identical situations to my own to now look to their consciences and abandon their disreputable campaigns.

“I know of dozens who know deep down what they’re doing is wrong. They should announce they are voting for the Labour or Lib Dem candidate who can win - and urge their supporters to do likewise.”