Peter Mandelson explains his resignation to Political Editor Robin Oakley

Trade and Industry Secretary Peter Mandelson, one of the prime minister's closest advisers, resigned on Wednesday after it emerged that he had borrowed £373,000 from Paymaster General, Geoffrey Robinson, to buy a house when the pair were in opposition.

Mr Robinson quit his post within hours of his Cabinet colleague, making this the first time that two ministers had resigned on the same day since 1982.

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Speaking for the first time since leaving his position at the Department of Trade and Industry, Mr Mandelson told the BBC: "Through my own misjudgement I've allowed the impression to be created of wrongdoing.

"I'm not going to allow that charge to be made against a government that I care about more than anything else in the world."

The row had gained impetus because the DTI is currently investigating alleged irregularities in Mr Robinson's business dealings.

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Mr Mandelson said: "I should have foreseen that in government that if people learned of this how it might appear, especially when questions were raised for the DTI to look in to questions about Geoffrey Robinson's business affairs.

"I should have been open about it - and in so doing I would have protected myself from the appearance of a conflict of interest.

"I didn't and I have paid a very big price for it."

But he said he could not guarantee he had not given false information on a separate mortgage form over which questions have also been raised.

"I have not checked on the form. I cannot clarify that even now," he said.

"I would just like to assure people I don't try to evade questions or mislead people and I hope I did not on this particular occasion.

"But it's not the reason - neither that or any other factor that might be revealed - that I've decided to resign today."

The Deputy Prime Minister, John Prescott, would not comment on speculation that one of Mr Mandelson's political enemies inside the Labour party had leaked information about the loan to the Guardian newspaper.

"I'll leave that speculation to the press," he told the BBC.

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On Channel 4 News Mr Prescott reacted angrily to suggestions that a key aide of Chancellor Gordon Brown informed on the former minister as part of a running feud within the cabinet.

"If all you are saying is, there's tensions between different groups in government, well yes, there may well be tensions between different groups," he said.

"That is not giving proof at all that such a serious allegation was made by an individual of one team against another."

Mr Robinson, in his resignation letter to the prime minister, said that after enduring 12 months of "a highly charged political campaign" he had decided to resign.

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Opposition MPs had been calling for Mr Robinson to resign for months after he was forced to apologise to the Commons for not properly declaring numerous business interests.

Mr Robinson told the BBC: "I think from the government's point of view, there comes a point [where] there's such an intensity of continuing allegation people get fed up with it."

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But he rejected the suggestion that his position had become untenable.

Cabinet Office Minister Jack Cunningham said the resignations had been "honourable" but sad.

"It is a great pity, a great sadness, for me and the government that this year has ended in this tragic, sad and unacceptable way."

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But Conservative leader William Hague insisted the prime minister should have fired Mr Mandelson and Mr Robinson.

"If these people were on my frontbench I would have sacked them," he said.

In his response to Mr Mandelson's resignation letter, the prime minister said he expected to see his colleague back in the government soon.

Mr Robinson and Mr Mandelson's resignations now bring the number of ministers to quit the government to five.

Mr Mandelson is replaced at the DTI by Treasury Chief Secretary Stephen Byers, whose job is taken by Health Minister Alan Milburn.

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