Britain's opposition Conservative Party, gambling public distaste for the euro can turn round its sagging election fortunes, said yesterday converting to the single currency would be five times the cost of dealing with the Millennium Bug.

Conservative finance spokesman Michael Portillo, whose party has ruled out joining the euro for five years, said it would cost as much as 36 billion pounds ($51 billion) for Britain to scrap the pound and enter the single European currency.

Prime Minister Tony Blair's Labour Party, which is sympathetic to euro entry, dismissed the figure as "worthless" and said no estimate was possible or feasible until there was a decision on whether to join the euro.

Trailing by up to 25 points in opinion polls for June 7's general election, the Conservatives attack on the euro question has put Blair increasingly on the defensive.

It has also pushed Blair into revealing far more details than he wants of his euro plans at a time when opinion polls show that nearly 70 percent of Britons want to keep the pound.

Portillo said because the Conservatives would keep the pound, they would use the money Labour would spend on conversion to give tax relief and increase public spending.

He quoted figures from accountancy firm Chantrey Vellacott which Portillo said showed the cost of conversion, which takes place in other EU member nations next January, would amount to 1,500 pounds for every household in Britain.

The 36 billion pounds figure was calculated by Chantrey Vellacott last year in a report for the anti-euro group Business for Sterling.

"Because we will keep the pound, we will not have to spend billions of pounds on scrapping the currency," Portillo said.

"It is astonishing that Labour is pressing ahead with its plans to scrap the pound while giving no indication of how many billions of pound this would cost the British economy."

The estimate was based on introduction of euro coins and the cost to businesses.

Portillo said a survey of large companies had shown: "If Britain were to join the euro the cost of altering computer systems would be five times as great as the cost of dealing with the Millennium Bug."

Labour's Chancellor of the Exchequer Gordon Brown said the report cited by the Conseravtives was "not worth the paper it is printed on".

Blair said: "This is just the usual Tory nonsense."

Blair favours joining the euro after the election subject to the right economic conditions and approval in a referendum.

In another attack on Labour's Europe policies, Conservative Party league William Hague said Blair would rig the question on a euro referendum to ensure a "yes" vote.

Hague has portrayed the issue as a turning point in British history and described the election in ten days time as effectively a referendum on the euro.

"The battle lines are very clear," Hague said in campaign speeches yesterday. "A re-elected labour government, by hook or by crook, will scrap the pound."

However Blair's support for the euro received a boost from major business leaders yesterday.

Chris Gent, chief executive of Vodafone (VOD.L) _ the world's biggest mobile phone operator _ and six other prominent company bosses announced their support for entry to the euro.

The economic benefits of joining would "enhance rather than undermine our sovereignty", they said in a letter to the Times.

Other signatories included Anthony Nelson, a trade minister in the last Conservative government and now vice-chairman of the Citigroup Bank (C.N), and Michael Bishop, chairman of British Midland BMID.UL.