The UK is entering into talks with three tax havens, as part of moves officials hope could help raise £10bn over the next five years.
The Treasury is seeking to claw back billions of pounds in undeclared funds from British citizens.
Discussions are already taking place with Switzerland about imposing a tax on new deposits and Liechtenstein has agreed to help British officials.
The three new tax havens involved in the talks have not been identified.
The Financial Times reported that Jersey, Guernsey and the Isle of Man had all denied being approached by the Treasury.
Switzerland, famous for its banking secrecy laws, is expected to introduce a tax on new deposits by British citizens.
A deal signed in August 2009 between HM Customs and Excise and Liechtenstein was aimed at targeting £3bn in offshore accounts belonging to 5,000 British taxpayers.
The government says it hopes £10bn could be brought in from the three tax havens, Liechtenstein and Switzerland between now and 2015.
Chancellor George Osborne said: "We are all in this together, and that includes those who try and evade tax. We are in the process of striking a deal with Switzerland and more deals will follow.
"In total, this will raise many billions of pounds which the previous government failed to do. This is tough but fair."