Did anyone see TweedleCam and TweedleClegg on the doorstep of Downing Street? I'm glad I didn't have breakfast this morning. Otherwise, I think I'd have been sick by now. (Will their private secretaries, by the way, be able to tell them apart?)

Nick Clegg - the former aide to Tory Eurocrat Leon Brittan and former member of the Cambridge University Conservative Association - is now the Deputy Prime Minister of the UK. David Laws - the former investment banker and Orange Book supporter of an insurance-backed health service who was once suspected by Paddy Ashdown of being a Conservative mole and was once invited by George Osborne to join the Tory Shadow Cabinet - is the Chief Secretary to the Treasury and Osborne's number two. Vince Cable - another former Orange Booker and one-time supporter of "light-touch regulation" who, as I noted in a critical NS profile of him in September 2009, first touted the possibility of a Tory-Lib Dem alliance back in 2005 - is the Business Secretary. It will be interesting to document Cable's verbal and intellectual contortions in the coming days, as he defends the impending Tory "austerity" measures - like Gordon Brown and Alistair Darling, he spent much of the election campaign condemning Cameron and Osborne's economic illiteracy and, in particular, their Hooverite enthusiasm for spending cuts this year (opposed, incidentally, by the IMF, the OECD and 67 leading economists in a letter to the Financial Times). So here comes the double-dip recession - courtesy of Cameron and Clegg, Osborne and Cable (oh, and those self-destructive Labour tribalists, on left and right, who preferred to luxuriate in opposition than contemplate a power-sharing deal with the Lib Dems).

The truth is that in countless seats seats across the land, thousands of people voted Lib Dem in order to keep Cameron out of Downing Street. They did not want, or expect, the Liberal Democrats to become Tory enablers in a hung parliament. In an interview with me on the eve of the election, the arch-tribalist Ed Balls called on Labour voters to back the Lib Dem candidate (and sitting MP) Norman Lamb in the Tory-Lib Dem seat of Norfolk North, in order to keep the Conservatives out. The result? The third-placed Labour vote fell 3 per cent and Lib Dem Lamb held onto his seat with an increased majority over the second-placed Conservatives. In my view, Lamb now owes those tactical Labour voters in his constituency an apology. So do all those Lib Dem MPs who were elected in three-way marginals.

Clegg has betrayed progressives across the length and breadth of Britain. He had a once-in-a-lifetime opportunity to repair the century-old rift on the centre-left and forge a radical and progressive alliance in favour of electoral and constitutional reform. I suspect Labour will now sit on its hands in any future referendum and the Lib Dems might be on their own campaiging for a "yes" vote. Their new partners in government have already stated their plans to oppose any change to our dysfunctional first-past-the-post system.

Clegg has also betrayed the longer-term strategic interests of his party, for crude and short-term tactical gains. Thanks to his bravura performance in the first TV debate, we had seemed to be on the verge of breaking our stale duopoly and introducing genuine three-party politics to the UK for the first time. But the next general election, whether it is sooner or later (and the bookies have 50:50 odds on another election within the year!), will see the Lib Dems horribly squeezed by the two main parties. It will be a straight Conservative-Labour battle once more. And what, after all, would be the point of voting Lib Dem? In fact, I'm sure the Labour pamphlets have already been printed: "Vote Clegg, Get Cameron". It has a ring to it. It also has the virtue of being true.

Clegg's decision to join hands with Cameron's Conservatives is, in the words of Alastair Campbell on Newsnight yesterday, "a strategic error of gigantic and historic proportions". Reports have already emerged of the Labour Party website crashing under the pressure of new membership applications. One Cabinet minister expects hundreds of defections from the Lib Dems to Labour in his own constituency. "I even know the names of one or two Lib Dem councillors thinking of jumping ship. They are distraught," he tells me.

Labour now remains the only truly progressive, centre-left, anti-Conservative mainstream party in this country. Bring on the next election. The Liberal Democrats will be punished. Clegg and co will regret their foolish betrayal.

Update: Oh, and the biggest policy betrayal by the Lib Dems was Clegg's decision to swap his effective amnesty for illegal immigrants for (what he once called) the Tories' "arbitary cap" on immigration. How can Lib Dems like Simon Hughes and Charles Kennedy vote for such an immoral and unworkable proposal?

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