LONDON - British Prime Minister David Cameron admitted Saturday he had mishandled the controversy over his shares in his father's offshore business interests, which were flushed out by the "Panama Papers" revelations.

Cameron said he would publish his tax returns and shouldered the blame for the row over his financial affairs.

Cameron and his Downing Street office issued four comments regarding the Panama Papers before the premier on Thursday finally admitted he had held shares in his late father's Bahamas-based offshore investment fund.

"It has not been a great week. I know that I should have handled this better, I could have handled this better," he told his Conservative Party's spring forum in London. "I know there are lessons to learn and I will learn them. Don't blame Number 10 Downing Street or nameless advisers; blame me."

On Thursday, Cameron admitted he and his wife had held a stake in his father's Blairmore Holdings scheme. They bought the stake for £12,497 in 1997 and sold it for £31,500, four months before he became prime minister in 2010.

The revelations in the Panama Papers, resulting from what the Panamanian law firm Mossack Fonseca blamed on a computer hack launched from abroad, revealed how the world's wealthy stashed assets in offshore companies.

Demonstrators gathered outside Downing Street later Saturday to call for Cameron's resignation. The protest, in which many waved banners saying "Cameron must go", briefly blocked the street outside the venue, with delegates advised to remove their identification before leaving.

"The facts are these: I bought shares in a unit trust - shares that are like any other sorts of shares and I paid taxes on them in exactly the same way," Cameron told his party's gathering.

"I sold those shares. In fact, I sold all the shares that I owned, on becoming prime minister.

"And later on I will be publishing the information that goes into my tax return, not just for this year but the years gone past because I want to be completely open and transparent about these things.

"I will be the first prime minister, the first leader of a major political party, to do that and I think it is the right thing to do."

Cameron's candid admission of fault, during which he said he had been angered at how the media had portrayed his late father, comes after a torrid period for the Conservative government.

Divided over a June 23 referendum on whether to remain in the European Union, forced to backtrack on welfare cuts and criticised for not protecting the steel industry, Cameron sought to rally party unity ahead of regional elections next month.

"We have a huge responsibility over the coming months and the coming years to settle this issue over Europe ... to show the discipline and unity and purpose that is vital for government," he said.

But the splits over Europe were in plain sight at the party's spring forum - a key event in the party calendar at which members discuss future policy.

Outside, before the event began, rank and file Conservative Party members had to walk between lines of rival "In" and "Out" campaigners offering bags of campaign literature, with each side cheering when a delegate took one of their leaflets.

Inside, chief "In" campaigner Cameron and de-facto "Out" campaign head Boris Johnson tried in vain to avoid the debate.

"Boris and I agreed we weren't going to talk about Europe. Did Boris keep his promise?" Cameron said to laughs from the audience soon after Johnson referred repeatedly to the referendum in a speech at the event.

London Mayor Johnson, who opted in February to oppose Cameron and campaign for a British exit from the EU, called June 23 "independence day" during his address.

Interior Minister Theresa May, making the final public speech, urged members not to let the EU debate dominate the party's term in office.

"The referendum is a question to which the answer will define our country for years to come," she said. "But we mustn't allow it to define our Party. Being a Conservative is more than about being Leave or Remain."