The June 9 declaration on euro membership will be a "momentous" occasion, Gordon Brown has said.

On Thursday Downing Street sought to end weeks of rows and speculation by setting out the decision timetable in the run up to the announcement.

The official spokesman said the final decision would be taken by "the whole Cabinet and it will take account of all relevant factors".

Number 10 declined to be drawn on whether the Cabinet will be able to overrule the Treasury's economic assessment, but senior ministers were said to be pleased at their key role in the decision-making process.

"There will be a constructive discussion and a consensus will be reached," said the Number 10 spokesman. "No final decision has yet been made."

And the chancellor told Sky News that the discussion process was "absolutely as it should be".

"This is a huge economic decision...it is momentous for the future of our country," Brown said.

This weekend the 2000 pages of 18 technical documents will be released to Cabinet ministers so they can consider their responses.

The prime minister and chancellor will then hold a series of tri-lateral meetings with individual ministers next week.

There will then be what is being described as a "second reading" of the euro issue among ministers at Cabinet on May 22 and department chiefs will consider the issue further over the half term Whitsun recess at the end of the month.

An assessment of the discussions so far will then be circulated among Cabinet members on May 26 which will then be followed by a second round of trilateral meetings between Gordon Brown, Tony Blair and individual ministers from June 2.

A special Cabinet session will then take place on June 5 or 6 where the final decisions will be made on the euro and the government's wider European strategy.

The announcement will follow on June 9, though it was not immediately clear whether Brown or Blair would deliver the statement to MPs.

Number 10 indicated that the final decision, through the process set out, would come from the Cabinet rather than the Treasury's assessment of the five tests.

"There is a distinction between an assessment and a decisions...a decision is not an assessment," explained the official spokesman.

There was also an implicit rejection of Clare Short's accusation that Tony Blair governed in a presidential style.

"This is a process which shows Cabinet government at work," said the spokesman. "This is a collective Cabinet decision."

Amid reports that the government is likely to rule out an immediate move towards joining the euro, the Conservatives warned against a damaging "fudged decision".

Shadow chancellor Michael Howard said that the eventual announcement could lead to damaging economic uncertainty.

"The reality is that any final, fudged decision made by Tony Blair and Gordon Brown won't be made on what's best for Britain but on the outcome of personalised faction fighting within Labour. It is time Labour put Britain's national economic interest first before their own internal factions," he said.

"The chancellor must rule out a rolling assessment. What Britain needs now is certainty to enable business to invest and create jobs. Anything less would be a betrayal of Britain's national economic interest."

And as the row over possible euro membership continued, a leading think tank said the time is not yet right for Britain to join.

The Institute of Public Policy Research said on Thursday that even though the exchange rate was around the right level, the UK should not join the single currency until the European Central Bank had been reformed.

In a boost to what is thought to be the chancellor's stance, the researchers said that European economic institutions present too much of a risk and are not sufficiently accountable in their present form.

However the centre-left think tank did concur with the Blairite position that the government should publish a "clear road map" to membership.

"There are likely to be real economic benefits for the UK in adopting the euro under the right conditions," said report author Richard Brooks.

"Less exchange rate uncertainty and greater price transparency within Europe should be good for UK trade, investment, jobs and growth, although the size of the positive impact is not clear.

"Joining the euro at the wrong exchange rate would be an expensive mistake, so getting the rate right should play a key role in the government's economic assessment."

The Treasury is also likely to support the IPPR's view that the ECB "and especially the stability and growth pact are real barriers to UK membership".

"The current UK monetary and fiscal policy framework is superior in many respects," the IPPR report found.

"The UK should not join the euro in the hope of achieving reform from within: this would be taking an unnecessary risk and talk about a 'window of opportunity' is misplaced."