

I remember a conversation with someone about 10 yrs ago that described the situation quite well
Conservatives turn the screws for 2 or 3 terms. Labour get in for a term to loosen the screws a quarter turn to let the country rest a little bit before the conservatives get back in to continue turning again
The UK ones are in a wierd rental deal where if I remember correctly the us holds at least 1 of the keys
Edit for a link https://www.bbc.co.uk/news/uk-68357294
While making the calculation look complex enough that the unwashed masses won’t question it