Lisbon Treaty Referendum - 319 is the magic number.

I've been crunching the numbers to see how many Labour and Lib Dem rebels are required to win the vote for a referendum on the Lisbon Treaty. Of the 646 seats in the house, a maximum of 637 are likely vote on the referendum (the Speaker and his deputies [4] don't normally vote, and Sinn Fein [5] don't have a vote). The only way to work this out without it getting over complicated is to assume all 637 will vote YES or NO. I'm going to divide the MPs into YES (in favour of a referendum) or NO (against a referendum) camps. I will add the known Conservative rebels [3] to the NO camp because it's almost certain that they will vote against a referendum. Everyone else will be assigned as per their party policy:

YES Camp total 212.

Democratic Unionist 9
Independent 2
Scottish National 6
Plaid Cymru 3
Conservative 190
Independent Conservative 2

NO Camp total 425.

Labour 352
Liberal Democrat 63
Independent Labour 1
Independent 1
Conservative 3
Social Democratic & Labour Party 3
Respect 1
Ulster Unionist 1

You can see that the NO camp has a majority of 213. Doesn't look good does it? This means that to win the referendum vote 107 MPs are required to rebel against their parties - the magic number being 319 votes to guarantee a win for the YES Camp.

In reality not all MPs will vote. Some will abstain (Labour and Lib Dem), especially those who are worried about losing their seats in the next election (they will be able to claim that they did not vote against a referendum). That being the likely case, then the number of rebels required will come down. I think a rough estimate would be that 90 to 95 rebels are required.

The question is: How many rebels are there? We know that there are quite a few likely to rebel on the Labour back benches, but what about the Lib Dems? There will be some, but Clegg is putting pressure on them to obey the Whip.

Can it be done? Does anyone out there have any idea of the rough number of Labour and Lib Dem rebels?