In what amounts to an 1,800-word manifesto days before David Cameron holds a global anti-corruption summit in London the source singled out the Conservatives saying they had been ‘shameless about concealing their own practices involving offshore companies’.
Cameron was forced to disclose last month he held shares in Blairmore, his father’s offshore investment fund.
More than 40 countries are due to attend the summit on Thursday.
The source behind the Panama Papers got in touch last year with Bastian Obermayer an investigative journalist with Germany’s Süddeutsche Zeitung newspaper.
They used the name John Doe and sent the message: ‘Interested in secret data?’
The source gave Süddeutsche Zeitung leaked documents from Mossack Fonseca’s internal database in real time instalments.
The papers included details of the beneficial owners of offshore companies – passport copies and emails.
The newspaper shared the material with the International Consortium of Investigative Journalists (ICIJ) in Washington.
In one of the biggest collaborations in journalistic history the ICIJ gave access to the data to 100 media organisations in 83 countries – which spent a year investigating them.