Has anyone changed research area to somehing completely different and started again as an undegrad?

undergrad or Mphil?

Undegraduate BSc

Rationale?

Begin dooing what you want to do now. We are not living an enternity.
We have only this moment....
My current PhD drives me crazy so i want to change direction and do something i ve always liked.

I take it you're not without a few quid then?

No i don't have any money to waste, yet i can't affort wasting my life doing something that i don't like (PhD) and that causes me severe depression

but why a BSc? you can change your PhD research area.

or do a conversion masters.

Hi, if you really believe you choose the wrong career and are convinced you should start again doing what you really like, do it. You can not be harming yourself doing something you don't like for the rest of your life. But just reflect for a moment if you are doing this because of frustration with the project (or supervisor or whatever...) or simply because you finally realized this is not for you. Try to be objective, when we are depressed, sadness and frustrations and blames do not let us see the reality as it is... Good luck and peace of mind.