European reaction to Britain's support for the war in Iraq will not influence the decision on whether Britain joins the euro, Gordon Brown has said.

The chancellor has also dismissed "unattributable gossip" that the Cabinet is split over the timing of a possible referendum on the single currency.

During Treasury questions on Thursday he confirmed that 18 background reports and the final assessment of the five tests would be announced by the first week of June.

There has been concern that continuing to exclude Britain from the euro would further alienate European partners and diminish the UK's influence in debates over future institutional changes.

Reports suggest that the prime minister is keen to keep open the option of a referendum before the next general election as an olive branch to European Union allies.

Labour backbencher Graham Allen warned the chancellor that to go for a referendum early and fail "would be the worst of all policies".

He added that "recent events with our European partners over Iraq" had made joining less likely in the short term.

Brown responded that the government would take "a long term decision about the future of Britain".

"It should neither be made on short term considerations based on foreign policy or based on other events that are happening this year. It should be made on a long term of the national economic interests," said the chancellor.

For the Conservatives, Michael Howard said other ministers were "gearing up for a concerted attack on the Treasury" in a bid to push for euro membership.

"Isn't it clear that the Cabinet is in complete disarray over this issue?" asked the shadow chancellor.

He added that analysis of the tests would depend "on the outcome of the furious faction fighting within this divided Cabinet".

But Brown dismissed "unattributable gossip" and said he would concentrate on the real issues.

Liberal Democrat spokesman Matthew Taylor warned that Britain's share of inward investment into Europe had been falling since the euro was launched.

Conservative backbencher John Bercow said the five tests had not been met and the public was opposed to euro membership.

He said the government should abandon any plans "to hand over massive powers for ever to people who we do not elect and cannot remove" and instead concentrate on improving public services.

But Brown said he would take "no lessons from Conservatives" either on European policy or on running public services.

"There are some people like the Conservatives who, even if it were in the national economic interest, would refuse to join as an act of dogma.

"And there are some like the Liberals who would want to join irrespective of whether the five economic tests were met. Our position is the right one," the chancellor told MPs.

Brown also said that the European stability and growth pact should be reformed to take into account investment, the economic cycle and the sustainability of governmental debt position.

"I'm pleased to say that opinion in Europe is moving in our direction in all these matters."