Boris Johnson is being urged to explain how the refurbishment of his Downing Street flat was paid for, following allegations from his ex-chief advisor.
Dominic Cummings claimed the PM had once had “possibly illegal” plans to get Tory donors to fund the work.
The government said “costs of wider refurbishment in this year have been met by the prime minister personally.”
But Labour said he needed to fully disclose who paid for the work in the first place.
Party leader Sir Keir Starmer said: “Publish the details, have the full inquiry. If there’s nothing to see here… have a full inquiry.”
“Every day there’s more evidence of this sleaze and frankly it stinks,” he added.
It comes amid a row over the lobbying of ministers, including the prime minister, after it was revealed he had exchanged text messages with businessman Sir James Dyson.
Once Mr Johnson’s closest ally, Mr Cummings was forced out of his Downing Street role at the end of last year, following an internal power struggle.
In a blistering attack on his old boss, Mr Cummings questioned the prime minister’s “competence and integrity”.
On Friday, in his first blog post since leaving his role, Mr Cummings:
- denied leaking text messages sent between Mr Johnson and Sir James
- denied leaking details of the second coronavirus lockdown in England in November
- alleged Mr Johnson had considered trying to block an inquiry into the leak in case it involved a friend of his fiancee Carrie Symonds – a claim rejected by No 10
- claimed the prime minister once had a “possibly illegal” plan for donors to pay for renovations of his Downing Street flat
Mr Cummings promised to answer questions about “any” issues when he appears before a Parliamentary inquiry into the government’s pandemic response on 26 May.