Another British prime minister has fallen for the illusory attractions of a referendum on Europe. Indeed Tony Blair’s decision to offer a plebiscite on the EU constitution is part of a depressingly familiar pattern. Gradually as their difficulties mount, the offer of a referendum seems like a blissfully convenient device or an unavoidable concession. Sooner or later the dramatic U-turn does not deliver what it promised. Instead the policy reversal lands the leader in even more trouble. Referendums are the equivalent of the femmes fatales in dark thrillers. They appear to lead prime ministers to the Promised Land, only to clobber them over the head as they attempt to get there.For Mr Blair the Promised Land could not be clearer.

The offer of a referendum deprives the Conservatives of an ace card in this summer’s European elections. No longer can Michael Howard argue that Mr Blair is too arrogant to consult the voters. Instead Mr Howard will have to focus on the implications of his own opposition to the constitution. This will lead the Conservatives on to some dangerous terrain.With the click of the prime ministerial fingers the new policy also clears the legislative path at Westminster. The House of Lords in particular will be deprived of trouble-making ammunition. In a year’s time Mr Blair will be able to fight a general election campaign in which Europe is once more a separate issue, one to be resolved in a referendum at a later date.

This may be enough to secure the support of Rupert Murdoch and his Eurosceptic newspapers for a third election campaign. At the same time the prospect of Mr Blair fighting a pro-European referendum campaign will reassure those who have been alienated by his timidity over Europe in the past and his passionate alliance with the United States. After the next election is safely out of the way Mr Blair could proceed to win a referendum and secure his historic objective of settling Britain’s ambiguous relations with Europe. He could leave Downing Street on a high.Except that the offer of referendums does not produce such smooth consequences. Mr Blair has given up some control of the situation and handed it over to fate, events and the unpredictable whims of the electorate From now on nothing will go quite as planned.

This is the dark lesson from the past 25 years.In holding a referendum on Britain’s continued membership of Europe in 1975, Harold Wilson had hoped to unite his warring party and settle the issue for a generation at least. In spite of winning by a big margin he achieved neither objective. By 1980 Labour was resolved to withdraw from Europe, one of the policies that provoked some senior figures to set up the SDP. Wilson had papered over the cracks for a year or two at most.When John Major promised a referendum on the euro in 1996, peace broke out in his party for around 10 minutes. Soon the Conservatives were fighting once more over Europe, for the good reason that divisions over the substance of a policy do not go away and are often exacerbated by the promise of a vote over the issue.Tony Blair’s similar pledge to hold a referendum on the euro was more productive in the short-term. It got him through two general election campaigns by making the euro a non- issue.