I want to have electric meters in each bedroom?

Tendency is to think that you use much less than everybody else. I think that all my neighbors should have meters on their irrigation water. They let it run down the gutter for hours. Well, if we all put meters on, it would cost 100 times as much for water. Soooo, I (don't) mind paying a little more for water to be a good neighbor. I do ask them to adjust misdirected sprinklers and help them fix broken pipes and sprinklers. Maybe you could agree with your room mates to limit consumption or pay proportionally.

Realistically just set some rules , you all share the house , who uses more water than someone else ? who uses the tumble drier etc.

It just gets too complicated.

Just share the bill equally, or if someone uses a lot more than someone else , try to agree to something like they pay £20 more than the other person etc.

Share the bill equally between you would be the easiest thing.

not going to happen, since the cost outweighs the advantage.

Before any one suggests a plug in monitor, it only has to be unplugged.