Both UCLA and Berkeley are part of the University of California, which is a public university, and the State of California requires the University of California to offer a place to all California students who make a certain score on the SATs/ACT and/or have certain grades. Not everyone gets to go to Berkeley; most people end up with an offer from a lower ranked UC school. But the grades and test scores for out of state and international students are higher than for instate students since the UC system has to take a certain number of California students.
I don't know how they factor in grades for UK students, but it is possible to be considered for admission (they would still look at your extra curricula activities and grades) by test scores alone. To give you an idea, there is a minimum formula which is on their website,
http://admission.universityofcalifornia.edu/counselors/freshman/minimum-requirements/examination/If you qualify by that standard, you likely have a very good chance, since this calculation basically ignores your grades, and if you have A*s that can only help.