The firm is understood to have instructed UK law firm Osborne Clarke to bring breach of confidence proceedings against both media organisations.

In a statement, an Appleby spokesperson said: ‘Our overwhelming responsibility is to our clients and our own colleagues who have had their private and confidential information taken in what was a criminal act.

‘We need to know firstly which of their – and our - documents were taken. We would want to explain in detail to our clients and our colleagues the extent to which their confidentiality has been attacked.

‘Despite repeated requests, the journalists have failed to provide to us copies of the stolen documents they claim to have seen. For this reason, Appleby is obliged to take legal action in order to ascertain what information has been stolen.’

A hacking attack on Appleby, which has which has offices in Bermuda, the Isle of Man and a number of tax havens, resulted in the publication of some 13.4m files which then became the subject of an investigation by the International Consortium of Investigative Journalists (ICIJ). The ICIJ partnered with the BBC and the Guardian to publish some of the material.

A BBC spokesperson said: ‘The BBC will strongly defend its role and conduct in the Paradise Papers project.  Our serious and responsible journalism is resulting in revelations which are clearly of the highest public interest and has revealed matters which would otherwise have remained secret. Already we are seeing authorities taking action as a consequence.’

The Guardian said the legal action was an attempt to ‘undermine responsible public interest journalism’.

The Paradise Papers contained information about how a range of ultra-wealthy individuals invest cash in offshore tax havens, and included details of how Formula 1 racing driver Lewis Hamilton avoided paying VAT on a £16.5m luxury jet, as well as a tax avoidance scheme used by three stars of BBC sitcom Mrs Brown's Boys.