An independent investigation must be held into the tax affairs of those implicated in the Panama Papers data leak, including David Cameron's family, Jeremy Corbyn has demanded.
The Labour leader said the leaks had exposed tax avoidance on an "industrial scale".
Downing Street has insisted that the business affairs of Mr Cameron's late father Ian, which were detailed in the Panama leak, were a private matter.
But Mr Corbyn told reporters in Harlow: "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.
"So an investigation must take place, an independent investigation."
Mr Corbyn said: "I think the Prime Minister, in his own interest, should tell us exactly what's been going on."
Speaking at Labour's local election launch event, he told reporters he wanted an investigation conducted by HM Revenue and Customs "about the amount of money of all people that have invested in these shell companies or put money into tax havens and to calculate what tax they should have paid over the years".
Asked whether the PM should resign if he is found to have benefited, Mr Corbyn said: "Let's take one thing at a time. We need openness, we need an examination, we need a decision after that."
Pressed on whether he would publish his own tax return, Mr Corbyn said: "There is no problem with my tax affairs, they are very, very limited indeed. I have got an income as an MP, sadly I have got no family trusts of any sort."
The Labour leader also suggested the Government could intervene to take direct control of the UK's offshore tax havens.
"If it's necessary for ministers to intervene because the governments of the Overseas Territories won't act, they can use an order in council to take control of them immediately," he said.
Mr Cameron's father ran an offshore fund which avoided ever having to pay tax in Britain by hiring a small army of Bahamas residents - including a part-time bishop - to sign its paperwork, according to the Guardian.
Ian Cameron, who died in 2010, was a director of Blairmore Holdings Inc, which, until 2006, used unregistered "bearer shares" to protects its clients' privacy.
His use of the firm to help shield investments from UK tax helped build up a significant legacy, part of which was inherited by the Prime Minister.
There is no suggestion that this avoidance arrangement or others exposed by the leak were anything but entirely legal or that Mr Cameron's family did not pay the UK tax due on any repatriated assets.
The Prime Minister has championed the transparency agenda at a series of international summits, and legislation forcing British companies to disclose who owns and benefits from their activities comes into force in June.
But despite several years of pressure, few UK Crown Dependencies and Overseas Territories - said to make up a large part of the tax havens referred to in the papers - have taken concrete action to open up the books.