Mm, I think it'd be very difficult in the UK system to provide a formal legally workable definition of X and not-X in your example, but I can see the argument for that.
Our biggest underlying problem, I think, is our voting system, in any case - it's largely responsible for locking most MPs into the two main party structures and giving them strong incentives to stay there no matter how venal, corrupt, or accepting of bigotry their party leadership are. Changing from FPTP to STV is the second longest standing liberal/lib dem policy, and one of the largest reasons I joined the party (in what seems now like a more innocent time, as grim as 2015 already was, before the word "Brexit" was a regular fixture in our politics).