Leading financial institutions have welcomed a new crackdown on international tax dodging agreed by Europe’s biggest five economies.
Tax and law enforcement agencies in the UK, Germany, France, Italy and Spain have agreed to share data.
But critics said it would only work if the US and other nations signed up.
Meanwhile, UK Chancellor George Osborne told the BBC that an agreement on an “international blacklist” of tax havens would be drawn up.
It came as the G20 group of nations, featuring some of the most powerful economies, said it would welcome such a list of proscribed havens.
“That means the whole world can take action against those who aren’t playing by the rules, and the world has just got a much colder place for those hotspots of international tax evasion,” Mr Osborne told BBC business editor Kamal Ahmed.
UK overseas territories such as the British Virgin Islands have been in the tax spotlight, and Mr Osborne said “they will definitely be on that blacklist if they don’t comply with the rules”.
Earlier International Monetary Fund’s chief Christine Lagarde said the five-nation initiative had added to the momentum building against those who sought to hide income and assets.
It comes in the aftermath of the Panama Papers leak, which revealed how the rich and powerful hide assets, sparking widespread condemnation that the authorities had failed to act.
Under the new deal, the five nations will exchange information regarding beneficial ownership registers, which show who really owns assets.
They will also create new registers of financial trusts.
The anti-corruption group Transparency International (TI) welcomed the move to open up trusts as well as companies, and that the data sharing would be automatic.
But TI said: “Nobody in this group apart from the UK has committed to public registers of beneficial ownership which experts agree are critical and has to be the next step.”
It added: “This announcement is significant because it recognises the big picture of trans-national corruption and illicit financial flows and shows real intent, but it is a very long way from being the end game.
“Although they have committed to getting more countries on board, the US is notably absent.”
Analysis: Andrew Walker, economics correspondent, BBC World Service
The initiative is directed at a problem that has come under a very bright spotlight with the release of the Panama papers, hiding income by using shell companies whose ultimate beneficiaries are unclear.
The wider international effort to combat tax evasion (illegal) and avoidance (legal) puts a great deal of emphasis on exchange of information between tax authorities, because concealing information from one’s home authority is an important tool for minimizing tax bills.
The new move applies to only five countries so many, probably the great majority, of tax motivated shell companies won’t be affected. But it is a start. They want the rest of the G20 leading economies to take similar steps.
And we can expect smaller tax havens to be leaned on to co-operate.
The chief of the International Monetary Fund Christine Lagarde said: “The IMF very strongly welcomes and supports this new momentum to fight corruption and tax evasion… we at the IMF will question whether the technical assistance that we provide to anti-money laundering and to counter-terrorism financing can be better leveraged to identify what more is needed in terms of implementation.”
The five countries will now push for the rest of the G20 nations to follow suit. That would mean sharing data on previously secret tax information between countries such as the US, Saudi Arabia and China.
The UK government has already announced that it will make its register of beneficial ownership public – and is privately urging the other four signatories of the deal to agree that the public can have access to the information, according to the BBC’s economics editor Kamal Ahmed.
The agreement was announced at joint press conference of the finance ministers of the five countries at the IMF.
Mr Osborne was joined by other finance ministers, including Germany’s Wolfgang Schaeuble and France’s Michel Sapin.
However, sharing data is not a simple process, experts say. Richard Murphy, director of Tax Research UK, welcomed the deal – especially Germany’s decision to sign up, as the country had always had reservations about sharing data.
But he said: “The big problem is that quite simply the UK is not collecting this information from its own tax havens and I don’t believe it’s going to.”
He said that there are 400,000 companies in the UK that do not provide ownership information to Companies House, and none of them are prosecuted: “So to suggest that we can share data with these other countries is at this point in time quite ridiculous. Until we get our house in order this is a hollow promise.”
The OECD group of leading economies said it was important to confront the financial experts that help the rich to evade tax.
Its head, Jose Angel Gurria, said: “We have to crank down on the professional enablers – lawyers, accountants, financial institutions and the like who play a key role in maintaining the veil of secrecy.
“This also means to ensure the loopholes which allow them to hide the beneficial ownership of companies, trusts and other arrangements. We have to make sure that those are closed.”
It comes almost two weeks after the leak of 11.5 million documents which revealed how businesses, politicians, and criminals used secretive companies to hide tax.
The fall-out from the so-called Panama papers forced Iceland’s prime minster to step aside.
And earlier Spain’s acting industry minister Jose Manuel Soria said he was resigning after alleged links to offshore companies in Panama and Jersey were disclosed.
Mr Soria denied wrong-doing, but said he was stepping down to limit any damage to the government.