David Cameron could face a leadership challenge from his own backbenches if Scotland votes in favour of independence, as Tory rebels blame him for presiding over the break-up of the Union.

The Independent understands that discussions have already taken place among Tory MPs considering standing a candidate against the Prime Minister if the Yes campaign is triumphant on 18 September.

The idea of a ‘stalking horse’ triggering a leadership challenge is widespread in British political commentary. It’s easy to see why: the idea of the brave challenger following in the footsteps of Margaret Thatcher or Michael Heseltine to challenge an unpopular leader, forcing a leadership election that would be a clash of the big political beasts is catnip to political commentators, enabling them to completely forget any kind of discussion about policy and talk entirely about personality and the election as a big game.

The problem with this vision is that it’s not actually possible in any party. The ‘stalking horse’ was a foible of the Conservative Party’s leadership election rules that disappeared when William Hague reformed the system after his election, and Labour and the Liberal Democrats never had a system that allowed it. The quirk in the Tory rules was that they didn’t require all potential candidates in a leadership election to be in the race from the start, but allowed them to enter at later rounds of the contest. As such, a stalking horse candidate could challenge the leader, and if they received sufficient support, other candidates could enter the race.

This was something that purely belonged to the Conservative leadership rules, and was in place because the decision was only made amongst MPs. Once parties put the leadership question to the wider membership, When an election’s a simple ballot in Westminster, it’s easy to have multiple rounds with different names, but if you’re balloting the entire membership, a set process and single ballot is a lot easier to administer.

The other reason for stalking horses disappearing is that they’re not a very good way of running leadership elections. There are two parts to the process of removing an incumbent leader: first, deciding whether you want the current leader to continue or be replaced; second, if they’re replaced, deciding who should replace them. The old Tory system conflated those two parts of the process, so that anyone wanting to remove the current leader had to vote for the stalking horse, but that vote could then make the stalking horse the leader, who the voter might like less than the current leader.Effectively, every vote has to be cast tactically, which might make for good drama but doesn’t mean they’re making the best decision on who’s going to be leader.

All the main parties now have systems that separate these two parts of the process, and none of them have a system that allows for stalking horses. So, if you hear or read a supposed political expert talking about stalking horses and leadership challenges, they’re letting on that they don’t understand the processes they’re commentating on. Someone can challenge a leader all they want but the rules now (especially for the Tories) mean they can only get them removed, not face them head to head.

(A couple of interesting books on leadership elections and structures, if you want to know more: Stark’s Choosing a Leader and Quinn’s Electing and Ejecting Party Leaders in Britain)