The prime minister has lost his nerve over joining the euro, the Conservatives claimed yesterday.

Responding to Tony Blair's new year message, Michael Ancram, the shadow foreign secretary, claimed that the prime minister believes he cannot win a referendum on the single currency and would use the five economic tests as an excuse not to join.

In a setback to the pro-euro campaign, a split has developed at the top of Amicus, the largest private sector union.

Although Roger Lyons, the co-general secretary, insisted that a survey showing that a slim majority of members favoured joining the single currency meant that "Amicus members would vote for the euro", Derek Simpson, the other co-general secretary insisted that nothing had been decided.

Simpson said: ""No one has spoken about the loss of democracy through membership of the euro and there has not been enough debate on the subject. There won't be a referendum this year and there is not enough information being discussed yet."

Meanwhile, Denmark, one of Britain's fellow opt-outs, has signalled it would hold a referendum on euro membership sometime after 2004 or 2005.