Fortunately for Tony Blair, it's easy to change a policy that hasn't involved the deaths of thousands of innocent people and even easier when you have Rupert Murdoch urging the change. It was no coincidence that the first reports of the referendum U-turn came in The Sun and The Times.
I can well believe they were the result of a telephone conversation the PM had with the media tycoon.
The anti-referendum line never had the support of the majority of the Cabinet in any case, especially Jack Straw and Gordon Brown. The policy was just plain stupid and would have been a complete PR disaster. It always plays badly with the voters to refuse them a choice over such big issues.
Way back before the 1997 election when Labour had yet to make a decision on the line to take on the euro, many MPs were still hostile to offering a referendum. Certainly Brown was reluctant to support a referendum since he, like all chancellors, wanted to take the decision himself. Brown eventually decided that it would be politically smart to offer the nation a poll, especially as the Tories were not only divided over the euro but hadn't promised the people a vote.
That policy has worked so well for Labour that Brown was determined to win Blair over to the idea of a referendum for the European constitution, too. There was one proviso - it would have to be delayed until after the election. The Chancellor had bitter memories of the devolution referendum held in Scotland just before the lost 1979 election.
Politicians may hate making U-turns, but for all the media bluster about it, by the time there is a referendum the only issue will be about our future in Europe. If Baroness Thatcher wasn't so determined not to U-turn over the poll tax, she probably wouldn't have gone so quickly.
Blair wants to hang around for a little longer yet.
The added bonus to this particular U-turn is that, once again, the Tories are wrong-footed. Michael Howard can bluster as much as he likes about holding a referendum now, but since we don't know what the final deal on the constitution will be, this isn't possible. The PM likes winning and he clearly thinks he can win this one.
The polls may look bad just now but that's because there has not been any debate yet, just a daily barrage of xenophobia from some of the tabloid press. Political commentators may have been taken by surprise by Blair's policy change, but the only real surprise is that he didn't make the decision earlier.