An article has appeared in The Independent which refers to a not-for-profit company set up to encourage people to vote-swap in order to target the Tory leadership. Whilst demonstrating the fundamental instability of 'First Past the Post' (changing the vote from candidate C to Candidate B can mean that Candidate A is helped, or hindered), such a tactic is fundamentally flawed. The simple reason is that the ballot is secret. There is no way, other than trust, to enforce such an agreement.
What's to stop someone promising to vote $arbitrary in return for the other person voting for $chosen? Indeed, such a promise could be made many times over... Other than as publicity stunts, such schemes are fundamentally flawed. For example, in my area, if you don't want the Tory MP you need to vote Lib Dem.
Personally, I'm more concerned with Labour getting a huge majority than with throwing the Tories into disarray, for all their faults, they did not make fundamental attacks on civil liberties.