One of the main reasons why Liberal Democrat support for the Coalition has been so solid is that they voted for it.  The Parliamentary Party did so.  So did a special conference.  So did the party’s federal executive.

If a second blue/yellow arrangement is proposed on Friday or after, the Conservatives have a chance to learn from what happened in 2010.  Neither Tory MPs nor party members then had the opportunity then formally to vote for coalition.  The question of its legitimacy has dogged the party ever since.

It is thus very much in David Cameron’s interest that there is a secret ballot of all Conservative MPs on any proposed coalition dealand, we believe, one of party members too.  In these circumstances, it will take place in any event: sources confirm that the 1922 committee executive is set on holding one (rightly).

The smoother the co-operation between Number 10 and the ’22 is if such a plan is put, the more likely it is to pass.  As I have written before, I believe that Party members will endorse a deal if Tory MPs do, and that the latter are likely to do so if one is agreed.

This is certainly so if our monthly survey is anything to go by.  As Henry Hill reported earlier this afternoon, over three in four Party member respondents to our latest questionnaire would be willing to see a second Conservative-Liberal Democrat Coalition (a four per cent rise on last month).

No fewer than four in five of those respondents would be willing to countenance a confidence and supply deal with Nick Clegg’s party.  All this helps to explain why a secret ballot may be Cameron’s key to Downing Street’s door – and why his team should signal that, in this eventuality, one will take place.