The chancellor has denied reports that he is set to rule out British membership of the euro.

With the government set to announce by June whether it believes the five test on entry into the single currency have been passed, Gordon Brown said the official assessment had not yet begun.

Analysis of the five tests would be "rigorous and comprehensive" the chancellor pledged.

He rejected suggestions in the Sunday Times that he had made a clear decision not to join the euro.

"This is not correct," he told BBC1's Breakfast With Frost. "The assessment has actually not started."

"We are doing a tremendous amount of work. This is the most difficult, the most important economic decision that this country has had to make on economic policy."

The Treasury is conducting 18 separate studies before it begins the official assessment.

"We are determined to do it on a rigorous and comprehensive analysis. The assessment itself has not yet started. The first report of the results will be to the House of Commonsand not to a newspaper.

"And I believe that when people see the work that we've done they will know that it's not just comprehensive and rigorous, it's looked at all aspects of the effect on the British economy."

Brown pledged the final decision would be made by the June deadline.

"We will publish all the studies. People will see for themselves. We've looked at trade, the effect on the housing market, on business investment, the capital markets, the flexibility of the European economy and the British economy.

"All of these are part of this assessment and it is detailed, rigorous, as you would expect and demand that it was."