Will more than half the Conservative Parliamentary Party follow Cameron into the Aye lobby this evening?

By Paul Goodman
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All free votes are free votes, but some are less free than others.  Today's same-sex marriage bill vote will help to prove the point.  The programme motion will be whipped.  So, as Philip Cowley and Mark Stuart point out this morning, will some votes be at committee and report.  The Second Reading vote won't be completely free from whipping, either - or at least a form of it.

The Whips Office is officially neutral on Second Reading. (Indeed, a chunk of the office will vote against it).  And there is a lively backbench whipping operation against second reading.  But with both David Cameron and George Osborne in favour of the bill, and effectively controlling patronage between them, requests to "help" the Prime Minister today have a certain status.

As I pointed out this morning, the Chancellor has been reported to be working the phones.  (He has form.)  So given the lead that he and Cameron have taken, what level of support would count as a success for the leadership at Second Reading?  The calculation isn't a simple one, because of the trade-off between a free vote and Downing Street "encouragement" that I describe.

• 306 Conservative MPs were elected in 2010.  Take away Corby, and that leaves 305.  Take away Nigel Evans, the Conservative Deputy Speaker, and that leaves 304.

• A quarter of that total is 76.  If a vote were officially whipped, for the Prime Minister to fail to get a quarter of his MPs to follow him through the lobby would be disastrous (as the EU referendum vote was, in which 81 Tory MPs defied the whip.  But allowance has to be made for the fact that Second Reading will not be officially whipped.

• A third takes us to over 100.

• And half is 152.  If the Prime Minister can't persuade more than half his own party to follow his lead when the Second Reading comes this evening, it will be a very bad result for him - even allowing for the absence of official whipping.