Gordon Brown has pledged Labour will not repeat the mistakes that were made by joining the ERM.

On the eve the single currency announcement, the chancellor reaffirmed his pro-euro credentials but warned he did not want to suffer the same fate as the Thatcher government.

Then prime minister Margaret Thatcher took Britain into the ERM but at a rate that was too high, eventually leading to Black Wednesday which forced John Major to reverse the decision and was a key reason for the Conservatives being forced out of office.

"We've been desperate to avoid the mistakes that were made when Britain joined the Exchange Rate Mechanism," Brown told the BBC on Sunday.

"Right at the centre of it is what is the national economic interest for the future and that is why the five tests are so important.

"In principle I want to join the single currency. In practical terms, we have got to be sure that all the conditions are in the right place and we don't make the same mistakes of the ERM era."

Though giving no hints about a decision that is expected to rule out a referendum for now, Brown did reveal the long-term deal that had been reached with the pro-euro members of the Cabinet.

"Tony Blair and I have decided, and the Cabinet agreed on Thursday, that after the statement tomorrow, we should put the pro-European case," he said.

"We have got to sweep aside the anti-European prejudice that Iain Duncan Smith is putting forward. The idea that we have got to choose between Europe and America is quite ridiculous."

The Conservatives attacked the government for playing "word games" over the euro.

Michael Howard claimed the government's two most powerful figures were putting private battles before national interest.

"This weekend Labour will continue to play word games over the euro. Whatever the final fudged deal, it's clear that Britain's national interest is coming a poor second to Labour's internal battles," the shadow chancellor said.

"It is fundamental to Britain's national economic interest for business to have a clear decision on the euro - yet, judging by government briefing, that is the one thing we will not have."

The Treasury's 18 background studies will be published on Monday morning at 9.00am, with the detailed assessments published immediately after the chancellor has concluded his statement to MPs.