Leading article: Shine a light on these dark recesses

Angel Gurria, the Secretary General of the Organisation for Economic Co-operation and Development, sounded like someone who could not believe his luck yesterday. Asked about the unprecedented attention given by G20 leaders in London to tax havens, Mr Gurria remarked: "We've had more progress in the past two weeks on this matter than we've had in the past 10 or 12 years."

The pledge from the leaders of the world's principal economies to demand transparency from tax havens certainly represents a remarkable shift. It has long been convenient for larger states to shunt the issue of reform into the sidings.

A little tax leakage from national treasuries seemed like a marginal problem when growth was strong. The technical difficulties of co-ordinated reform did not seem worth the effort.

But now treasuries everywhere need every penny they can get. And after the banking collapses and scandals of recent years there is a new willingness among leaders to shine a light on the dark recesses of global finance.

The new determination to bring tax havens into line is welcome. For decades these enclaves have laundered drug profits, aid stolen by African dictators and the earnings of corrupt businessmen; not to mention allowing the very richest in society to pay less than their fair share of tax.

But a question mark remains over how effective the measures announced in the G20 communiqué this week will be. The summit proposed sanctions against tax havens that do not transfer financial information on request. But it gave no details of what action will be taken against offending territories.

The OECD has produced a list which names and shames those enclaves and nations that are not co-operating with international accounting rules. But there has already been a fudge over the treatment of Macao in order to placate Beijing.

Moreover, the promises from tax havens to abide by internationally agreed tax standards do not mean a great deal. These regimes have formidable experience in the art of obfuscation. They will doubtless fight to shield the interests of their clients. The test of the G20's pledge to end "the era of banking secrecy" will be in the delivery.