The political marriage between Nick Clegg and David Cameron may be so strong that the idea of a future Lib/Lab Coalition looks rather fanciful.
And yet there are those in both parties who are gently blowing on the flickering embers of Lib/Lab cooperation.
Significantly a dozen or so Lib Dem former Parliamentary candidates and councillors have now decided to join the Labour Party's policy review.
This is an unprecedented step.
Many in both parties will probably be intensely suspicious of the move.
Some Lib Dems will suspect their colleagues are simply being used by Labour.
Some in Labour will be deeply sceptical about allowing their political enemies to contribute to their next manifesto.
But Richard Grayson, the Lib Dem's former head of policy who is among those joining Labour's review, says it is simply about breaking down tribal divisions on the left and sharing ideas.
It is, of course, also about building firmer bridges between Labour and the Lib Dems and opening up the possibility that after the next election the two parties could work together.
"We have to think about the prospect of a different coalition in the foreseeable future," says Mr Grayson.
"There has been much talk of 'the new politics' but unless we are prepared to engage with Labour then there is a danger that 'new politics' will simply mean working with the Conservatives."
From the Labour side too there is also a pressing need to forge better relations with the Lib Dems after they collapsed in acrimony in the days after the last election. And many in Labour still appear to enjoy nothing more than baiting and mocking Liberal Democrats.
Some senior voices in Labour, however, are keenly aware that they face an electoral mountain at the next election, particularly if the planned boundary review goes ahead, possibly depriving them of a further 20 seats.
And there is also a nagging worry that the electorate may have decided to bring to an end the era of one party government.
Hence the need to open up the possibility of a Lib/Lab coalition.
Publicly, of course, Labour figures are still careful to insist that they are fighting for an outright majority at the next election and that the cooperation with the Lib Dems over the policy review is simply about sharing ideas.
But the head of Labour's policy review Liam Byrne does not close down all talk of coalition.
"This is about making progressive politics stronger," he says, "And getting in place a coalition that votes for a more progressive kind of politics at the next election."
And there is a also wider momentum developing behind cooperation between the two parties.
The left wing think tank Compass is currently balloting its members on allowing Lib Dems to join; and thinkers from the two parties regularly share platforms and attend seminars together.
One Lib Dem think tanker told me that 80% of their joint work was with Labour-leaning organisations rather than Conservative groups.
What seems clear is that on the broad left of British politics there is a growing acceptance that, if the left is to win, it may have to start learning to work together.
After all, if Nick Clegg and David Cameron if can forge a coalition why can't the left?