Is my GCSEs good enough for Law

how did you perform compared to the rest of your year?

I want to study Law in Uni, preferably at a Russel group uni
Maths - 7
English lit - 6
English lang -5
History -7
Comp Sci - 6
Combined Sci - 66
Spanish - 5
Further Maths - 5
Drama - 5
I plan to take History, Politics and English Literature for A levels, might do an EPQ and intend on doing work experience in a Law Firm.

Congratulations on getting your results !! They look quite good to me, but no one can tell you for sure so I would just have a look on UCAS at the different entry requirements for each law school/ law degree at universities you're interested in to see what grades they want, I know some degrees want e.g. five grade 7's in any subjects in which case you might want to think about retaking a couple to boost up your stats or just look for a university with slightly lower entry requirements if you don't want to resit. Good luck and well done again !!

Would that mean no matter how I would perform in a levels my application would be denied due to not having strong enough GCSEs at certain unis, if so I might consider.

yes, depending on the university. It all depends on their entry requirements, some law schools care more about e.g. the law school admissions test, some want a certain grade in a certain subject at GCSE, others might just ask for a 5 in English and maths and then ask for e.g. AAA at A level, it all depends so research the requirements for the law schools you're interested in