Labour rising star Wes Streeting has denied preparing a leadership bid to replace Keir Starmer after it emerged that the wealthy party donor Waheed Alli hosted a recent fundraising event for him and another MP at his central London home.

The Observer has been told that the actors Ian McKellen and Michael Cashman, as well the businesswoman and LGBTQ+ activist Linda Riley, were among 20 to 30 people present at the event in March, where Lord Alli picked up the £4,600 bill for a buffet and drinks.

The event raised around £20,000 from those who attended, which was split between Streeting and his fellow Labour MP Kim Leadbeater.

One senior frontbench source said on Saturday that Leadbeater, the member for Batley and Spen and sister of the late Jo Cox MP, could be being lined up as a potential running mate with Streeting, for the post of deputy leader, were a contest to take place.

Some senior figures in the party, who do not favour Streeting as a future leader, say the shadow health secretary has been “on manoeuvres” for months, readying himself in case Starmer leaves his post before or after the next election.

Rumours about the activities of possible replacements to Starmer began swirling round Westminster last week after the Labour leader announced he would resign if fined by Durham police for drinking a beer and eating curry in an MP’s office after a day of campaigning for the local elections in April 2021.

While Starmer is confident he will be cleared, having received four different legal opinions on the case, his pledge to quit if fined has inevitably started several hares running on the subject of a possible succession battle.

Others thought likely to run if Starmer has to quit include the shadow levelling up secretary, Lisa Nandy, and the shadow home secretary, Yvette Cooper.

Andy Burnham, the mayor of Greater Manchester, said last week that he had not given up hopes of leading the party, though this would not be in the near future; first he would need to be selected and then elected to a Labour seat in the Commons.

Burnham made clear last week in an interview with LBC that were a future opportunity to arise, and the party wanted him, he would relish tackling the levelling up agenda and reforming the way the country is governed.

Streeting’s office vehemently denied that the event at Alli’s house had anything to do with leadership ambitions and said it was merely to raise funds for constituency campaigning.

A spokesman for Streeting accused people in the party of stirring up mischief, saying: “This was a joint fundraiser with Kim Leadbeater to support her campaigning in Batley & Spen and to support Wes’s campaigning in Ilford North and as shadow health secretary. Keir’s office were fully aware of the event, which was held months ago. Whoever briefed this nonsense should put their wooden spoon away.”

Streeting, who grew up in a council flat in Stepney, east London, and funded his way through Cambridge University by doing shifts during his holidays in the customer service department at Comet, has been the MP for Ilford North since 2015.

He is now widely regarded as one of Labour’s most effective communicators.

His allies point out that he has been one of the Labour leader’s most consistent advocates and defenders. Aged just 39, he is on the right of the party and was heavily critical of Jeremy Corbyn’s leadership.

Peter Kyle, the shadow Northern Ireland secretary and an ally of Streeting, said such events were normal and set up as a way to allow MPs to pay for extra staff whose salaries could not be met from party funds. “I can put my hand on my heart and say this had nothing whatsoever to do with any leadership shenanigans,” said Kyle.

Alli has been a long-term donor since he was first brought into the New Labour inner circle under Tony Blair and has funded the campaigns of successive leadership candidates, including David Miliband and Starmer himself. He gave £100,000 to Starmer’s campaign, which led to his election in April 2020.

The latest Opinium poll for the Observer shows that the so-called Beergate affair had led to a 10% fall in Starmer’s personal ratings over recent weeks. Despite this, Starmer is still regarded more favourably than Boris Johnson on issues relating to Partygate and Beergate.

Nine out of ten (89%) think that Johnson broke the rules during the pandemic, with 63% thinking he did so intentionally.

For Starmer, 58% think he broke the rules, with 30% thinking he did so intentionally. Two-thirds of respondents (65%) think he was right to say he would resign if he received a fixed penalty notice.

Adam Drummond, head of political and social research at Opinium, said: “A media focus on Beergate was never going to be the best talking point for the Labour leader after the local elections, and this is reflected in the hit to his net approval ratings that now sit at -10.

“Nevertheless, voters are much more likely to give Keir Starmer the benefit of the doubt that he acted appropriately than the prime minister, while almost a quarter have actually gained a more favourable view of him for the way he has responded to the accusations, by promising to resign if he is fined by the police.”