The move by the business leaders threatens to undermine the increasingly hostile Tory approach towards a European single currency, and will further strengthen Labour's position.
Sir Colin Marshall, president of the Confederation of British Industry and chairman of British Airways, denied their decision to write an open letter to the Financial Times was motivated by party politics. "We are concerned about the level of anti-European sentiment. And we are concerned it might get worse in the run-up to the election."
Other signatories include Martin Broughton, group chief executive of BAT Industries; Ross Buckland, chief executive of Unigate; Sir Ronald Hampel, chairman of ICI; Tony Greener, chairman of Guinness; Sir Richard Evans, chief executive of British Aerospace; and Sir Peter Bonfield, chief executive of BT.
"As business people operating not only in Europe but across the world, we have watched with dismay the spread of extreme Euro-scepticism and of the mistaken belief that an arm's length and hostile attitude on Europe is now in the UK's best interests.
"The reality is quite different. The UK must remain a full and committed member of the club."
They warned that the benefits from European Union membership would be put at risk if Britain chose isolation; Britain would be poorer, with lower investment and higher unemployment. They also warned that Britain's bargaining position at the EU summit in Amsterdam in June would be "gravely weakened" by Euro-scepticism.
That anxiety will have been increased yesterday by John Major, who told a Talk Radio phone-in that a Conservative government would try to block a "botched" European single currency.