Opposition politicians demanded an investigation of tax havens on Tuesday after an offshore investment fund run by Prime Minister David Cameron's father was among several British companies listed in the Panama Papers.
Cameron's office said the use of Panama-based lawyers Mossack Fonseca as part of a tax avoidance scheme by Blairmore Holdings Inc was "a private matter." His father, Ian Cameron, controlled the fund from 1982 until his death in 2010.
Labour leader Jeremy Corbyn said it was "not a private matter if tax has not been paid," adding that leaked documents from the law firm had revealed tax avoidance on an "industrial scale."
"It's a private matter in so far as it's a privately held interest, but it's not a private matter if tax has not been paid," Corbyn told reporters.
"So an investigation must take place, an independent investigation," he said.
The listing of his father in some of the 11 million leaked documents also prompted calls by British media and politicians for Cameron to explain the current status of the Panama-registered fund, close loopholes in British tax law and even repay the tax avoided.
"The prime minister should lead by example and come out and set the record straight on his own tax affairs - we need full and total transparency," John McDonnell, Labour's shadow chancellor, said in a statement.
Cameron said he had no offshore assets to declare, but he did not say whether or not he or his family had benefited from tax avoidance schemes.
"I own no shares, no offshore trusts, no offshore funds, nothing like that," Cameron said when asked about his father's company during a visit to Birmingham.
"I would say that no government, no prime minister, has done more [than me] to make sure we crack down on tax evasion, on aggressive tax avoidance, on aggressive tax planning, both here in the UK and internationally," Cameron said.
He did not comment on the listing in the Panama Papers of several British entrepreneurs and former politicians who have made large donations to his ruling Conservative Party.
McDonnell said the Conservatives "should come clean and set out exactly what the situation is - is the prime minister happy to receive money from big donors who are accused of tax avoidance?"
The Daily Mail, one of Britain's most popular tabloid newspapers, said the naming of Cameron's father and the Conservative Party donors was embarrassing because Cameron has "spearheaded efforts to make international finance more transparent."
Steve Richards, a political commentator for The Independent, said Cameron "cannot be held responsible for his father's financial arrangements," but argued that the leaks reflect "the powerlessness of elected power."
"When the super-rich have the power to avoid their fair share of tax, the elected rulers become even more constrained," Richards wrote in the newspaper.
Ahead of a June referendum on whether Britain should remain part of the European Union, he said the leaks were "a vivid illustration of why going it alone is not a viable option for a medium-sized economic power."
The International Consortium of Investigative Journalists (ICIJ), which analysed documents first leaked to German daily Sueddeutsche Zeitung, quoted a Blairmore Holdings prospectus for investors as saying the investment fund should be managed "so that it does not become resident [in Britain] for taxation purposes."
The ICIJ quoted the leaked documents as saying the fund had achieved its offshore status by using untraceable "bearer shares" held by nominees in the Bahamas, a practice that Britain outlawed last year.