Nick Clegg may be determined to remain equidistant between Labour and the Conservatives but his party's voters aren't. The latest Independent/ComRes poll shows that while 46 per cent of Lib Dem supporters would be happy with a deal that allows Gordon Brown to stay on as prime minister in a hung parliament, only 31 per cent would be happy if David Cameron became prime minister in these circumstances.
It proves that despite Clegg's line that both the main parties are as bad as each other, Lib Dem voters continue to recognise Labour as a more progressive force than the Conservatives.
It also suggests that any tactical votes from Lib Dems are still more likely to go to Labour than the Tories. Recent research by PoliticsHome found that, contrary to expectations, tactical voting could rise at the election.
But the main stumbling block to a Lab-Lib coalition remains the fact that Clegg's hostility towards Labour isn't purely tactical: he can't stand Gordon Brown.
The possibility that the Lib Dems will demand Brown's head as the price of any pact has been raised before and in today's Times, the well-sourced Rachel Sylvester suggests that Labour ministers are prepared to grant it.
With Cabinet ministers openly discussing the prospect of coalition, the question of the Labour leadership is back on the agenda. David Miliband is seen as the candidate most likely to appeal to Mr Clegg, although some point out that Alan Johnson has long supported the Lib Dems' favourite policy of PR. The suggestion is that the party's elder statesmen -- Lord Mandelson, Jack Straw or Alistair Darling -- could ask Mr Brown to stand aside to give Labour a chance of retaining power. It's hard to see him going easily -- but it is being discussed.
Given that Labour is famously sentimental towards its leaders (one of the reasons Brown survived all three coup attempts) and that to deny the Tories a majority would be a remarkable personal victory for him, Brown will be hard to shift.
But we can expect this question to become ever more prominent if support for the Lib Dems remains at anything like its present level.
Update: Sunny Hundal says that Labour should prepare to ditch Brown now.