I got A*A*A in Maths, Physics and Economics but know plenty of people who have gotten in with A*AA as well. Bristol says on their economics admissions page that "Applications are scored and ranked based on their academic record, according to their achieved or predicted results with the following weightings: GCSE 20% | A-Level 80%". Personal statement, work experience ect would only come in if there are making a call between the last few close applicants I'm pretty sure surprisingly.