John Rentoul: Cameron's problem? It's not the coalition, but his revolting MPs

The vote on Lords reform showed how Tory members are increasingly taking a stand on questions of principle. It's not good news for the PM

Storm clouds: Tories defied their party in an end-of-term Commons rebellion (EPA)

Surveying the wreckage the day after the biggest Commons rebellion since the last one, a Liberal Democrat minister said to me: "I don't understand. I thought the Conservative Party was the party of ruthless self-interest, prepared to do whatever it takes to win elections. But something happened at the time of Maastricht." The minister's view was that last week's Tory split had damaged the coalition, but its lasting effect was to make it harder for the Tories to win the next election. One of the Tory rebels, Jesse Norman, on the other hand, thinks that they were being "helpful" to the Prime Minister.

It just goes to show how differently politics looks from either side. From Lib-Dem Land, the Prime Minister reneged on a deal to deliver something that was in the coalition agreement, namely a "wholly or mainly elected upper chamber on the basis of proportional representation". From David Cameron Towers, on the other hand, the Lib Dems are guilty of having "moved the goalposts", by threatening, if they don't get Lords reform, to block the boundary changes, which favour the Conservatives.

And those are "two issues that the public don't care about", as a source close to the Prime Minister put it with some irritation.

For once, I confess to feeling some sympathy for Nick Clegg, though I care little about Lords reform and, to the extent that I do care, do not agree with his plan for a four-fifths elected Upper House. He thought he had a deal. He did have a deal. For Liberal Democrats, the coalition agreement is the "sacred text", as one of them put it to me. "Coalitions have to have a sacred text," I was told. That is how they work in continental Europe. But the difference between the Liberal Democrats and the Conservatives is that Lib Dem MPs and peers met and voted on the outline coalition agreement, and feel bound by it, whereas Tory MPs met and listened to David Cameron telling them what the deal was. They did not vote, or dip their hands in the blood, and as a result do not feel bound by the "sacred text" in the same way. Lib Dem internal democracy is much mocked, but sometimes it helps party discipline.

That said, a more sinuous politician than Clegg would have anticipated the problem of Tories believing in conservatism, and would have worked harder to win over potential Tory rebels. And a more persuasive politician would have defended the Bill with more charm and skill in the Commons.

It is no use complaining about how coalitions are run in the rest of Europe. Clegg should have been realistic about (a) what his partners could deliver, and (b) what is important. Lords reform is not important, except that it makes the Government look disunited and out of touch. But last week's rebellion was significant because, as my Lib Dem minister said, it suggests the Tory party is no longer the election-winning machine it once was.

Lords reform will soon be forgotten. The Bill will either be dropped or a minimal compromise will be agreed. But the high-minded rebelliousness of his party has more serious consequences for Cameron. After the revolt − 91 MPs defied the Whip, and 19 did not vote, in total a majority of all Tory backbenchers − it is not the coalition that is threatened, although it is damaged. It is the Tory party. The growing tendency of its backbenchers to take a stand on questions of principle has been reinforced. That kind of thing leads only to trouble.

It will be felt on another issue about which the voters care only slightly more than Lords reform: Europe. David Cowling, the head of the BBC's Political Research Unit, pointed out in an internal note last week that Ipsos-MORI polls this year have found that between 3 and 7 per cent of people mention Europe when asked an open-ended question about "important issues facing the country today".

Yet that was the issue that prompted that previous Tory rebellion, of 81 MPs in October, on a motion demanding a referendum on the EU. Cowling quotes Michael Ashcroft, the Tory peer, at that time. Ashcroft, who respects opinion polls and pays for a lot of them, wrote that the Tories had to do two things if they were serious about winning the next election: "To address the things they [the electorate] care about most, and to show that we are changing the things that put them off voting Conservative in the past …. It is futile to say we want to gain the extra support we need to win, and then act in ways that make victory less likely rather than more."

Cowling points out that, since the UK joined the Common Market in 1973, there have been 10 general elections, and the question of Europe played a decisive part in none of them. Yet it has divided both main parties in turn. "The past 40 years suggests that the issue of Europe is like weeping gelignite – both explosive and unstable and just as likely to blow up in the face of those who wield it as it is to destroy their enemies."

Last week's rebellion was not good for the coalition, but the passion of Tory MPs, especially those of the new intake, in standing up for principle above party suggests that Cameron has a more serious problem with his own party than with his coalition partners.

twitter.com/@JohnRentoul; independent.co.uk/johnrentoul