David Cameron faces demands to give a statement in Parliament setting out his financial affairs as he struggled to draw a line under the row over his connection to his late father's offshore business interests.
Labour leader Jeremy Corbyn said the Prime Minister has "misled the public" and "lost the trust of the British people" after admitting he had made a £19,000 profit from an offshore fund set up by his late father.
Mr Corbyn's strongly-worded intervention came as even the Prime Minister's allies conceded his handling of the row could have been better.
The Prime Minister sold his and wife Samantha's shares in Blairmore Holdings - one of the tax haven schemes exposed in the Panama Papers leaks - in 2010 and insisted it was not set up as a tax dodge.
He paid income tax on dividends but the £19,000 profit on the sale was insufficient to attract capital gains tax.
Mr Corbyn demanded "decisive action" against tax dodging which the Panama Papers leak revealed was taking place on an "industrial scale".
Mr Cameron has insisted it was a "fundamental misconception" that Bahamas-based Blairmore was set up by his father Ian to avoid paying UK tax and stressed that his interest in it had been "subject to all the UK taxes in the normal ways".
Pressure has been mounting on the Prime Minister for days after Downing Street initially claimed his financial affairs were a "private matter".
Mr Corbyn said "it took five weasel-worded statements in five days for the Prime Minister to admit that he has personally profited from an undeclared Caribbean tax haven investment deal".
Cabinet minister Michael Fallon conceded that Mr Cameron's handling of the row could have been "neater" but bizarrely appeared to blame the media for failing to ask the right questions - even though the Prime Minister and Downing Street had repeatedly been pressed to fully disclose his involvement during a torrid week for his leadership.
The Defence Secretary told BBC Radio 4's Any Questions: "I think it was a very difficult issue for the Prime Minister because it concerned his late father who he much revered.
"Of course it's true that if the fuller questions that were asked of him yesterday had been asked of him earlier in the week then it might have all been neater. But that is hindsight.
"What we know now, we know three things: first he had shares in this unit trust, which an awful lot of people in this country ... have through their private pensions and you pay taxes on those shares.
"Secondly, we know that he sold those shares before he became Prime Minister back in 2010.
"Thirdly we know that he paid all the taxes that were due when he sold those particular shares.
"I don't see that he has done anything at all improper."
Tory MP Victoria Atkins also suggested that Mr Cameron could have revealed he benefited from the offshore fund earlier.
Ms Atkins, who prosecuted tax fraud cases before becoming an MP, told Channel 4 News. "If we were to replay this week, who knows whether the Prime Minister would have had that interview a day or two earlier.
"But the fact is now he has been completely frank and transparent about his affairs."
But critics continued to heap pressure on the Prime Minister, despite his Thursday night admission that he benefited from the Blairmore fund.
Mr Corbyn said: "The Prime Minister has lost the trust of the British people. He must now give a full account of all his private financial dealings and make a statement to Parliament next week.
"Only complete openness from the Prime Minister, and decisive action against tax avoidance and evasion, can now deal with the issues at the heart of this scandal."
Scottish First Minister Nicola Sturgeon said while Mr Cameron had previously "talked a good game on tax avoidance, we've found out this week the reality doesn't always match the rhetoric".
She said: "I think David Cameron has given the impression that he's been trying to hide something over the past few days, he's had several statements and started by giving the impression there was nothing to hide before last night saying he had benefited from an offshore trust.
"I think he has to be completely open and transparent about this now."
Labour MP John Mann said he would report the Prime Minister to a sleaze watchdog, claiming he should have declared his shares in Blairmore in the register of MPs' interests.
Mr Mann, who has called for Mr Cameron to resign, said he would ask parliamentary standards commissioner, Kathryn Hudson to investigate.
A No 10 spokesman said: "The Prime Minister's interests have always been recorded in line with the rules as they stood at the time."