The UK Parliament works on the principle that each constituency elects a member to represent them. He/she is a representative, not a delegate, so the electorate chooses him/her, but has no control over how he will vote on individual issues. Once elected the members may form or join alliances, but are not obliged to do so. Political parties have no status within the system. You do not vote for a party (although you may think that you do.)The sovereign may invite anybody except himself/herself or members of the immediate family to form a government. That person may form any group or alliance to do this and this person does not have to sit in the House of Commons. The majority of leaders, whose appointment is called First Lord of the Treasury (for convenience, called Prime Ministers) in the nineteenth century actually sat in the House of Lords.
Political parties are a relatively modern phenomenon, and do not have to exist. In the past they were at best loose alliances. Possibly in the future the idea will be dropped. Benjamin Disraeli actively worked against Sir Robert Peel, but in theory they were both Tories.
The problem with proportional representation is that it assumes that you must belong to a political party before you can stand. It follows from this that we would need a fundamental rethink of our constitution before we can start to consider PR. Since our constitution is flexible and evolves by precedent this is not impossible, but let's not kid ourselves that it will be simple, whichever of the numerous systems we choose. And that's grounds for a lengthy debate in itself.
If you get PR, you cannot elect a representative, but a party would nominate delegates. At present we have a system of three line whips, but a representative may ignore its instruction (often at risk to his career), whereas a delegate is mandated and will be simple voting fodder.
Many MPs, including some leaders appear not to appreciate all this.
Be careful what you wish for; you may get it.
