HMRC is investigating claims that Britain's biggest bank HSBC has been storing millions of pounds belonging to some of the country's most notorious criminals.
It is believed that millions of pounds have been taken by the bank's operation in Jersey from crooks including drug dealers and computer hackers.
A spokesman for the bank said last night told the Telegraph that they were taking the allegations very seriously.
"We can confirm we have received the data and we are studying it," he said.
"We receive information from a very wide range of sources which we use to ensure the tax rules are being respected."
Shadow Treasury minister Catherine McKinnell said the government needs to show more urgency in tackling shadowy banking practices.
"These are very serious allegations. The chancellor must ensure that HM Revenue and Customs and the FSA investigate this quickly, have the resources they need to do so and take any action required," she said.
"We have been calling for more transparency in tax havens, but the government has so far been too slow to act.
"And this case underlines why we need major culture change in our banks as well as a much tougher approach to tax avoidance and evasion."
HMRC also confirmed the leaked document, but did not comment on any individuals on it.
The total amount on the list adds up to £699 million and contains over 4,000 names - including some well-known celebrities and public figures - with the average amount per account coming to £337,000.
HSBC were recently fined $1.5 billion in the US for breaking money laundering laws after cash was found to be illegally sent over the border to Mexico to avoid tax.
It is common for HMRC to pay whistle blowers for information that can lead to clamping down on illegal tax evasion, but in this case it is understood the list of accounts was handed over for free.
Jersey is often used as a proxy for legal tax avoidance. Earlier this year comedian Jimmy Carr was criticised by the press and the prime minister for sending over £3 million into a scheme based on the Channel Island to reduce his tax liabilities.