Anti-poverty campaigners have urged David Cameron to build on his agreement with Britain's network of Crown dependencies and overseas territories to forge a global deal on tackling tax evasion.
The Prime Minister hailed the agreement struck in talks in Downing Street with the leaders of the ten offshore jurisdictions on the exchange of information between tax authorities as a "very positive step forward".
He said he hoped it would strengthen his hand in negotiations at next week's G8 summit at Lough Erne in Northern Ireland where he has placed tax transparency at the top of the agenda.
"Let's be clear why this tax issue matters. If companies don't pay their taxes or individuals don't pay their taxes we all suffer as a result," he said. "It is important we are getting our house in order. It is a very positive step forward and it means that Britain's voice in the G8 and the campaigning on this issue around the world for proper taxes, proper companies and proper laws ... will be stronger."
Bermuda, the British Virgin Islands, the Cayman Islands, Gibraltar, Anguilla, Montserrat, the Turks and Caicos Islands, Jersey, Guernsey and the Isle of Man were all represented at the talks. Many of the islands and outposts are regarded as tax havens - a description they bitterly dispute - where wealthy individuals can shield their fortunes from the prying eyes of onshore tax authorities.
Under the agreement, they will trial an international pilot programme which will see the automatic exchange of information between tax jurisdictions while signing up to the Organisation for Economic Co-operation and Development's (OECD) convention on mutual assistance on tax. They also agreed to publish national action plans on beneficial ownership - declaring the true owners of so-called "shell" companies.
Anti-poverty campaigners welcomed the announcement but said they were only a first step in ensuring developing nations were able to collect the billions they were entitled to in tax revenues.
Melanie Ward, of the Enough Food for Everyone IF campaign, said: "David Cameron has today cleared a big obstacle to a clampdown on tax dodging, but a G8 agreement that will help the world's poorest is hanging in the balance.
"The acid test of the PM's efforts will be whether he delivers a G8 deal that clamps down on tax haven secrecy and phantom companies, and will help poor countries collect the money they need to end the scandal that sees one in eight people go to bed hungry."
Michael Elliott of the ONE campaign said: "We need to see more progress on these issues over the coming days. By taking these steps, the G8 can make sure that it not only puts its own house in order, but does so in ways that work for people beyond the G8 too."