Boris Johnson is facing calls to remove Alun Cairns as a Conservative candidate after the Welsh secretary resigned over allegations that a former aide sabotaged a rape trial.

Cairns stepped down following huge pressure in recent days over the actions of his former adviser Ross England, with the furore threatening to derail the Tory campaign in Wales.

The Welsh Conservatives had said last week that Cairns did not know about the conduct that led to a judge accusing England of deliberately sabotaging a rape trial. However, an email later came to light calling into question whether Cairns knew England could be in trouble over his actions.

Cairns sent a letter to Johnson on Wednesday saying he was confident he would be cleared by any investigation into his behaviour, but he was stepping down because it was such a “sensitive matter”.

Johnson thanked Cairns for his role in abolishing toll charges on the Severn Bridge and his “unstinting record of service for the party in Wales”.

However, Jeremy Corbyn, the Labour leader, said the prime minister should prevent Cairns from standing again to be an MP.

“First of all, there’s a victim here,” he told broadcasters after a speech in Telford. “That victim needs to be apologised to and needs to be supported.

“Secondly, if he’s resigning because of his behaviour and involvement in this as the secretary of state then shouldn’t he also be resigning as a Conservative party candidate in the election? That’s my question.

“Obviously, legally he can stand as a candidate, but does he have a moral right to stand as a candidate? If he’s stepping down as a minister because of his involvement then I would have thought the very least the Conservative party can do is not put him up as a candidate in the next election.”

Keir Starmer, the shadow Brexit secretary and a former director of public prosecutions, said: “He is right to resign but he has got to face an investigation. This is a very, very serious issue. It goes well beyond a ministerial investigation. Resigning was right to do but it is not enough on its own.”

Wales is full of key target leave-voting seats that Johnson needs to win to secure a majority.

On Tuesday, BBC Wales published an email it said was sent to Cairns by his special adviser, Geraint Davies, more than a year earlier, in which Davies wrote: “I have spoken to Ross and he is confident no action will be taken by the court.”

The email was sent on 2 August 2018, the BBC reported. Four months later, England was selected as the Welsh Conservative candidate for the Vale of Glamorgan for the 2021 Welsh assembly election. He was later suspended after being accused by a judge of deliberately sabotaging the rape trial. The rape victim is among those who called for Cairns to resign.

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On Wednesday, Mark Drakeford, the Welsh first minister and Labour leader in Wales, said Cairns’ position was another example of the Conservative party’s arrogance. He said it stood beside remarks by Jacob Rees-Mogg about the Grenfell fire and comments from a Tory candidate in Gower, south Wales, suggesting people on the reality TV show Benefits Street needed “putting down”.

Christina Rees, the shadow Welsh secretary, said Cairns’ decision to step down from the cabinet was “far from the end of the matter, and is a shoddy halfway house that will fool nobody”.

She added: “He has still not explained his behaviour and still not addressed the grave issues raised by the leaked emails yesterday. Worse still, neither he nor any senior Welsh Tory have apologised to one person who most deserves it: the victim herself. He should do the right thing: apologise, and step down as a candidate.”

Speaking after a visit to a factory in Watford, Jo Swinson, the Liberal Democrat leader, said: “It’s right that he’s resigned. The allegations that were made are incredibly serious and I think there are real questions to be asked about why it’s taken him so long to come to this conclusion, and why he said the things he did before. I imagine as time goes on we’ll find out the answers to some of those questions.”