With the current state of UK politics, I believe this is an idea whose time has come.
The UK government comprises members who won the most votes in their constituency. It is a simple system, but it favors parties whose votes are concentrated in certain regions. Parties whose support is spread evenly rarely reach a majority anywhere so they get very few seats even if they have a large voter share. Those with low support usually don’t get any seats at all, but if their support is mostly from a single area, they can win a seat. Whatever the merits of such a system, and there are some, it certainly isn’t ‘fair’ in terms of equal representation. With some constituencies bigger than others, some voters get far better representation of their views than others.
My suggestion is very simple. Firstly, each MP in parliament should have the value of their vote on each issue scaled to the national proportion of people who voted for that party. Secondly, so that all significant parties are represented, each party with more than 1% of the national vote should get at least one MP, even if none achieved a majority anywhere. So to take real examples, if the Green Party gets 2% of votes, but only one seat out of 600, then their MP should be given 12 votes. If the Labour Party, with 30%, gets 45% of the seats, then each of their MPs should only get two thirds of a vote each. If Conservative win 35% of the seats with 35% of the vote, they would get one vote each. That way, there would still be a good mix of MPs and each would still represent a constituency, but every voter would have equal representation, very unlike the current system. Minority parties would benefit greatly, and the big parties would have to suffer only getting the power they actually represent.
With such a system, it ought also to be possible to divide your vote, giving some of it to one party and some to another. That would immediately remove the problem where if the left or right vote is divided, that the MP the fewest people support can win the seat. They would still win that seat, but the voting power would still go to all the parties according to their actual support.
Naturally, some people would like this system and others would hate it. It is quite normal to want to keep an unfair advantage and upsetting when it is removed. But it is surely time to make democracy so that every voter has an equal say in the running of the country.