It is a relationship that has taken a battering since the 2010 election.

Yesterday Nick Clegg, standing in at Prime Minister's Questions for David Cameron, gave a potentially interesting insight into Liberal Democrat relations with the Labour Party.

Earlier this year it was reported the Deputy Prime Minister had enjoyed a cordial chat with Labour's shadow chancellor Ed Balls. The same Ed Balls, you remember, whom David Cameron tries to attack every time he stands up at PMQs.

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Mr Clegg had previously described the senior Labour politician as the only person with whom he had ever had a personal feud.

So a line-up of the LibDems' leader against Labour deputy leader Harriet Harman promised much.

On the one hand, Mr Clegg had to try to be robust and defend the Government's record. On the other, he could not afford to be too harsh on Labour - after all to Liberal Democrats opposition parties are just friends they have not been in government with yet.

Labour, of course, faced a similar quandary.

And there did appear to be fewer MPs on the Opposition Labour benches than usual (although they did their best to chunter loudly).

Behind Mr Clegg plenty of Conservatives turned out to hear the LibDems' leader's words of wisdom.

Were they hoping their hated Coalition colleague would make a gaffe at the Despatch Box? Or were they there to keep an eye on any growing rapprochement with Labour?

For his part Mr Clegg occasionally seemed to be channelling David Cameron. At one point as he described the Prime Minister's view on something a Labour MP shrieked "but what do YOU think?"

And any talk of thawing relations on either side should not be overdone. There were still plenty of accusations thrown on both sides.

Labour accused the LibDems of selling out to the Tories. Clegg accused Labour of having ruined the economy. In some ways, plus ca change.

But was the laughter just a little more hollow and muted than normal when one Labour MP, in a nod to the LibDems' council election defeat last week at the hands of the Elvis Bus Pass Party, asked Mr Clegg if his theme song should be "You ain't nothing but a lapdog"?