Sir Keir Starmer has said that under a Labour government, the prime minister, chancellor and deputy prime minister would all publish their tax returns.

The Labour leader told the Sunday Times that his party would also add greater transparency in publishing the internal register of ministerial interests, with the party considering using an opposition day debate this week to give Tory MPs a vote on the matter.

It comes as Downing Street grapples with the controversy surrounding Tory chair Nadhim Zahawi, as well as questions about former prime minister Boris Johnson and the appointment of Richard Sharp as BBC chairman.

Downing Street has said that Mr Sunak will publish his own tax return “in due course”.

I see no reason why the Prime Minister shouldn’t publish their tax return as a matter of course.

Sir Keir told the paper: “I think it’s pretty simple: those in charge of taxation can’t also be seeking to avoid it.

“I’m mystified why the Prime Minister couldn’t just say that this week. I see no reason why the Prime Minister shouldn’t publish their tax return as a matter of course. It happens elsewhere already.

“And if we are serious about restoring trust, I think anyone appointed as chancellor or deputy prime minister should do the same.”

Sir Keir added: “Trust in politics matters. It’s why I said from the start that if I were fined over Durham, I’d resign. It’s why we are committed to cleaning up Westminster. The public need to know that the swamp is being drained.”

Earlier, the Labour leader used a speech at London Labour’s conference to tell members not to be complacent about the battle to win the next general election, which Sir Keir’s party is widely tipped to do after the series of scandals and controversies that have plagued successive Tory administrations.

“The Tories will never give up on power,” he told members.

“That’s not who they are. So don’t let up. No complacency. Fight for every vote.”