Bristol law offer retraction

Like many leading Unis, Bristol will score each application and the rank all applicants for each course. They then make gradual offers working down that list - ie. the 'threshold' gets lowered as the admissions cycle progresses - until they have made enough offers to fill the course.
For Law, Bristol uses the weightings 20% GCSE, 40% A levels, and 40% LNAT. Were your GCSE weaker, have you taken LNAT yet, or did you feel that it went badly - remember that Bristol also reads the LNAT essay. Any of these could explain why they thought you had not met the threshold yet - however, its unusual for Uni to make an offer and then withdraw it, unless they have discovered something factually incorrect about your application. I suggest that you or your school phones them and asks for an explanation about this decision.

My gcses are weaker, but there were extenuating circumstances surrounding those.
I have taken the lnat, i feel the essay went reasonably well but the multiple choice i feel slightly less confident on.
My main confusion was just that I had the offer which got revoked almost out of the blue

I agree this retraction is very clumsy - and usually a Uni would just leave the offer in place and email you to tell you that the offer had been made in error but they would honour it. I think you do need to get your school involved with this - talk to your Head of Sixth or similar on Monday and ask them to call Bristol on your behalf.