A group claiming to champion transparent financial data says identities of “thousands” of people using Jersey-based accounts have been leaked.

A group claiming to champion transparent financial data, which in 2013 obtained client account details from the British Virgin Islands, says identities of “thousands” of clients of Kleinwort Benson in Jersey have been leaked to it.

“The individuals include donors to the British government, which has been outspoken against tax havens, and some of the most prominent people in British life,” the International Consortium of Investigative Journalists said in a statement. The group said it allowed the Guardian newspaper – which has published such material before – to analyse “more than 20,000 of the names, all of whom had dealings with a discreet Jersey, Channel Islands branch of Kleinwort Benson”, it said.

This publication is in contact with Kleinwort Benson about the matter and will update in due course. It has also contacted Jersey Finance, the organisation representing the island’s financial services sector. It has so far not commented on the matter.

The group, which claims it campaigns to shine a light on the offshore world, did not explain how it was able to obtain the data, or who leaked it, or when. Such leaks in the past, involving the names of thousands of people, have prompted angry responses from jurisdictions such as the BVI, saying that legitimately private data has been put in the public domain. The issue raises the thorny question of what is the correct boundary between secrecy and legitimate confidentiality. (This issue is most acute in Switzerland.) It also raises questions about whether genuine tax planning activity is any longer possible in a world where policymakers increasingly blur the distinction between illegal tax evasion and tax avoidance.

The ICIJ itself noted that the actions of the persons in Jersey are not illegal, but “unfair”, which might suggest the ICIJ's own stance is politically motivated.

The issue is particularly toxic from a political angle because several of the people whose information has been leaked are public figures, as well as celebrities, legal figures and other prominent individuals.

“In the interests of transparency, ICIJ and The Guardian will publish some of their findings over the coming days, detailing the offshore links of political donors; international celebrities; judges; sportsmen; businessmen; and British aristocrats,” the ICIJ statement said. “Names range from vacuum cleaner tycoon James Dyson to Hollywood actor Mel Gibson. Today The Guardian identifies party donors who over the years have paid more than £8 million to the governing Conservative party,” the statement continued.

“One of the recipients of donations is Britain’s newly-promoted financial services minister, Andrea Leadsom, who has run into a `Cash for Office’ allegation after she told The Guardian she was unaware of the size of large offshore donations to the Conservatives made by her own  family,” it said.

The group previously published secret internal records of offshore companies in the British Virgin Islands in 2013.

“We make this information available not because what we found is illegal but because we think most people would think it unfair. Tax havens allow some people to play by different rules,” ICIJ director, Gerard Ryle, said.