Mainly from categories like Car Insurance, Employment, Legal etc where the USA answer is useless for the UK?

Just go down to the bottom of the page and select UK from the list of countries.

and on the questions page for a category you can click show then make your selection it should list your english speaking country there

You can't avoid those answers, whens you ask a question from uk site & i switch all english question i'm able see your posts & answered.

Or simply disregard the answers you don't like or that are irrelevant.

For instance if you don't like this answer, don't pay attention to it.

Most simple way to go.