Most of the real power is in the budget, which is technically a bill, but I would 100% go for "change the voting system". Almost anything except D'Hondt is better than FPTP; for simplicity, we could just copy the Scottish Parliament's use of AMS.

I would also insert a trapdoor that future changes to the voting system would require the approval of >50% of eligible voters, including non-voters. Yes, I know Parliament cannot bind its successors and all that, but at least I can make it look bad to change it again.

Does this solve any of the immediate problems? No. Does it solve the dysfunctionality since 2008? I think so, especially given that polling these days looks like five parties getting 20% of the vote each. Labour themselves came to power on 38% of the vote.

Lots of the problems in the UK stem from a lack of strategic vision. More coalitions, infighting, compromises, etc aren't going to drive serious change home. Don't really care if it's Labour or Tory, tbh, just want national politics focus on bigger picture stuff and bulldoze through regs if it's a matter of strategic investment.

What would be nice for voting reform, is to add regional elections across the nation (replacing the old European ones). This would be a great layer of government to vote in coalitions, who deal with 'softer day to day areas of government' (care, benefits, roads, etc). Would be a great incubator for national talent, too. We should be able to see how future PMs deal with a region before trusting them with national affairs.

The grand coalition governments of the EU are not in any way better. They just result in bickering and gridlock because parties that hate each other get stuck in the same room.

This is your pet issue, completely based on the grass looking greener on the other side.