HMRC said early analysis of the data, totalling 400 gigabytes, showed extensive use of complex offshore structures to conceal assets around the world, including Singapore, the British Virgin Islands, the Cayman Islands and the Cook Islands.
The tax authority has identified more than 100 individuals benefiting from these structures, a number of whom are already under investigation for offshore tax evasion, reports The Telegraph.
More than 200 UK accountants, lawyers and other advisors will also be scrutinised.
HMRC stressed there was nothing necessarily illegal about the structures.
Jennie Granger, HMRC commissioner, said: “These arrangements may be perfectly legitimate and may already have been declared to HMRC.
“However they may involve tax evasion, avoidance or other serious offences by taxpayers. What has to stop is using offshore structures to illegally hide assets and income.”
Chancellor George Osborne said the data were “another weapon in HMRC’s arsenal”.
“The message is simple: if you evade tax, we’re coming after you,” he said.
HMRC is working with the US and Australian tax authorities to investigate the data. It said it was unable to comment on the source of the data.
Phil Berwick, a partner at international law firm Pinsent Masons, said individuals with any doubts about the legitimacy of their tax arrangements overseas would be “spooked” by the announcement.
“This is a clear warning shot against accountants and other advisers that HMRC is going to come after them if they are involved in establishing offshore structures.
“HMRC is keen to clamp down on accountants and other advisers who they feel have overstepped the mark.”
The Association of Chartered Certified Accountants (ACCA) said while it welcomed moves to clamp down on tax evasion, “we should never lose sight of the fact that it is a small number of people who are evading tax in these markets”.
Chas Roy-Chowdhury, head of taxation at ACCA, added: “The majority of accountants, lawyers and other professional advisers, as well as their clients, are not breaking any laws in these locations.
“There is a large gulf between what amounts to tax avoidance, which is within the law, and tax evasion, which is illegal.”