Labour's official position is that it is in favour of joining "in principle" - assumed to mean joining in the first wave, if Germany and France unite their currencies in January 1999, the timetable set by the Maastricht Treaty. Any retreat from that would dismay Labour's strongly pro-European wing, but would avoid trouble from the large minority of Eurosceptic Labour MPs in the early years of a Labour Government.
The Labour leader is sensitive to the difficulty of selling the single currency to voters becoming increasingly doubtful about Europe - and of winning a "Yes" vote in a referendum. He is also said to be tempted by the prospect of increasing Tory divisions by adding to pressure on John Major to declare against joining.
Robin Cook, Labour's foreign affairs spokesman, surprised some members of the party's National Executive on Wednesday by saying that the presentation of policy on the single currency would be "re- visited" before the general election, expected in May next year.
Sources close to Mr Cook said he is aware of the difficulties of getting through an election campaign with "the form- ula we have got now". One said Mr Cook recognised that the single currency decision might seem harder to "fudge" when the Treasury predicts in November's Budget whether Britain would be eligible to join.
Civil servants calculate that the British Government could effectively have to make the decision in the autumn of next year, just months after a general election, in order to get the necessary laws through parliament.
Mr Cook's supporters point to Labour's pre-manifesto, New Life for Britain, launched last month, as evidence of Mr Blair's growing scepticism. In a section written by the Labour leader himself, it says the issue "must be determined by a hard-headed look at its economic practicalities". It describes monetary union as "a major step of integration which in principle could bring benefits in terms of stability and lower interest rates".
It goes on: "For Britain, we would need to be convinced that economic conditions would allow it to succeed."
Mr Cook set out the disadvantages of joining the single currency at some length at an unreported Westminster book launch last week. Pointing out that Britain had failed to match German productivity growth over the past 30 years, he said: "Before we give up our currency, we have to be confident that we will never again need to devalue. In other words, we will never again over a long period of time fall behind the performance of Continental industries."
For many in the party, casting doubt on Britain joining the "first wave" is recognising a hard fact, but others, including shadow chancellor Gordon Brown, are worried about sending a Euro-sceptical signal to the markets, businesses and European governments.Reuse content