The shadow chancellor said he regretted sparking a row over alleged talks with Oleg Deripaska about a £50,000 donation, which engulfed his party and threatened his own job.

He spoke as a poll showed his standing in the country had plummeted.

Mr Osborne said: "I neither asked for money nor received any, but I did make a mistake. It didn't look very good, and I regret that."

Asked if he had shown a lack of judgment in his dealings with the aluminium baron, said to be Russia's richest tycoon, he replied: "I think the real judgment is, can you learn from mistakes you make?

"I have changed the way that I am going to operate when it comes to fundraising and I will not discuss individual donations with individual donors.

"That, I think, is an appropriate thing for me to do."

Mr Osborne was stripped of his fundraising role after discussions with David Cameron, the Tory leader, who reportedly referred to him behaving like a "prat" over the affair.

But Mr Cameron toned his down criticism yesterday, saying: "We have all learnt lessons from this. There is no doubt about that. George Osborne has been very frank about explaining what they are."

But last night, Geoff Hoon, the Transport Secretary, said: "George Osborne's judgment is wrong. And once again, it is because he creates headlines on the hoof without care for the consequences. His mistakes just go to show why this is no time for a novice."

Vincent Cable, the Liberal Democrats' Treasury spokesman, appeared more forgiving. "He (Mr Osborne] did show very bad judgment in meeting this guy (Mr Deripaska] five times. If he is effectively apologising, I am sure that is the line under his particular involvement."

An opinion tracker of 5,000 voters across the UK by PoliticsHome Phi5000, powered by YouGov, found Mr Osborne's approval rating had dropped from -11 to -20, making him the most unpopular high-profile Conservative.

But he was not the only one to be tarnished by his brush with Mr Deripaska. Lord Mandelson, the Business Secretary, on a trade visit to Moscow, was besieged by reporters questioning him about his meetings with the billionaire during his time as the EU trade commissioner.

Graham Watson, a Liberal Democrat MEP, said EU rules stated that a commissioner had to detail all hospitality received, even in their private life. "Peter Mandelson cannot hide behind an excuse of it being a holiday," he said.