Comment by michaelt

It's a good deal more complicated than that.

MPs belong to political parties - consider what happens if an MP's constituents and an MP's party disagree?

They might be allowed to vote against the government, if their vote will have no effect on the bill's passage - but if they actually stop the bill's passage? They're kicked out of the party, which will make the next election extremely difficult for them.

MPs are elected for reasonably long terms - and that means they regularly do things that weren't in their party manifesto. Nobody running for election in 2024 had a manifesto policy about 2025's strikes on Iran, after all!

That flexibility means they can simply omit the unpopular policies during the election campaign. A party could run an election campaign saying they're going to introduce a national ID card, give everyone who drinks alcohol a hard time, cut benefits, raise taxes, raise university tuition, fail to deliver on any major infrastructure projects, have doctors go on strike, and so on.

Or they can simply not put those things in their manifesto, then do them anyway. It's 100% legal, the system doing what it does.