By Mark Wallace
Follow Mark on Twitter
Their most awkward moment came as their leader stood in for the Prime Minister at PMQs. Veteran eurosceptic Edward Leigh brandished a Lib Dem leaflet from 2008, asking whether the person claiming to be Nick Clegg who promised "a real referendum on Europe" was "an imposter or a hypocrite"?
At the time, this was a pledge Clegg felt strongly about – going to the point of trooping his MPs out of the Commons when the Speaker rejected an amendment proposing an EU referendum.
Obviously his position has changed, and he now seems dedicated to stopping the people getting a say.
The Deputy PM's standard get-out nowadays is to point to his party's 2010 manifesto (with no justification for the change in policy since then). It said:
"The European Union has evolved significantly since the last public vote on membership over thirty years ago. Liberal Democrats therefore remain committed to an in/out referendum the next time a British government signs up for a fundamental change in the relationship between the UK and the EU."
That certainly justifies his support for the coalition's referendum lock, which guarantees a vote next time the EU proposes a treaty change which will transfer power to Brussels. But does it justify his commitment to wrecking Cameron's referendum plans? Well, no.
Let's look again at the manifesto pledge. It promises:
"…an in/out referendum the next time a British government signs up for a fundamental change in the relationship…"
That isn't a promise of a referendum only when powers go to the EU, or only when the European institutions are pushing the changes. It is simply a promise for a referendum whenever the British government signs up for fundamental change.
So if (a big if, but all the same) Cameron's renegotiation secures an acceptable agreement which will return powers to Britain, the Lib Dem manifesto pledge commits them to support an in/out referendum – which is exactly the policy Nick Clegg is now opposing.