Gordon Brown has denied "dithering" over Peter Hain, who resigned from the government yesterday after the Metropolitan police was asked to investigate his failure to report £103,000 in donations.
Mr Hain telephoned the prime minister to resign as work and pensions secretary and Welsh secretary immediately after the Electoral Commission said it would refer the secret funding to the Met.
The Conservatives had accused Mr Brown of showing poor judgement in not sacking Mr Hain sooner but today the prime minister insisted it had been right to wait until the commission reported.
Speaking to the BBC he said: "They have the facts, they were looking at them, they made the judgement and now we get on with the business.
"And the most important thing that people should know is that we're getting on with the business of government."
Mr Hain revealed at the end of November that he had not declared all the donations to his failed deputy leadership campaign.
This month he reported the full extent of his campaign spending to the Electoral Commission, including £50,000 donated through the apparently defunct thinktank, the Progressive Polices Forum.
A separate investigation by the parliamentary standards commissioner has now been suspended pending the police investigation.
Mr Brown said the reporting irregularity was an "incompetence" but insisted he had confidence in his work and pensions secretary.
Yesterday Tory leader David Cameron said Mr Hain's eventual resignation was the "right decision".
But he added: "The Prime Minister should have said to Peter Hain, 'you've got to give a convincing explanation of your situation or you can't stay in the Cabinet,' instead we've had a long delay where one of the most important departments in government hasn't been led properly."
James Purnell, who has replaced Mr Hain at the Department of Work and Pensions, denied the affair had left "a bit of a taint around the question of Labour's relationship with money".
He told the BBC Labour were keen to move forward with Hayden Phillips' recommendations on party funding.
Both the Conservatives and Labour accuse the other of stalling reforms, with the Tories demanding Labour accept a cap on union donations.