Oliver Wright: PM misjudged strength of feeling in his own party

When David Cameron decided to impose a three-line whip on Tory MPs for last night's vote on an EU referendum he miscalculated.

He assumed the traditional combination of party loyalty, hope of promotion and fear of the penalties would keep any backbench rebellion down to a manageable level. But for a number of reasons – including genuine principle, political advantage and a difficult relationship with his own backbenchers – the strategy failed.

In the first place, Mr Cameron appears to misjudge the strength of feeling on the issue among MPs. The present Conservative Parliamentary party is more Eurosceptic than at any time, its ranks swelled by a new intake politicised in the Thatcher years.

The problems in the Eurozone have emboldened Tory EU critics who believe that not only were they right about the single currency but they are also correct in their analysis that it is in Britain's strategic national interest to break away (at least in part) from Brussels.

But if that's the principle, then there was also a touch of political gamesmanship in last night's vote. The planned boundary changes and reduction in the number of MPs at the next election means many Tory backbenchers will have a fight to keep their seats.

Normally that might count in favour of the leadership – but grassroots Tory sentiment is overwhelmingly anti-European and these are the people who will decide who stays and who goes. In a poll by the website Conservative Home yesterday nearly three-quarters of party members said they wanted their MP to vote for a referendum. As one senior backbencher put it: "Who's more important in helping me keep my seat, my members or Tory HQ?"

Finally there is the changing face of the House of Commons and Mr Cameron's relationship with his own backbenchers. Many MPs feel unloved by the leadership. There are those who believe they will never achieve ministerial office because there are fewer jobs to go around in a Coalition and there is a perception that Mr Cameron favours the new intake.

The new intake is different from its predecessors and not just on Europe. They are less blindingly obedient, having been elected at a time when MPs were discredited by the expenses scandal, and less willing to follow unquestioningly into the Government lobby.

So what happens next? Mr Cameron may have won the vote – with Labour support – but he has entrenched divisions within his party. And that could spell further trouble for him in future.