There isn't a specific set of GCSE grades required to become a lawyer. The path to becoming a lawyer requires a degree, usually a law degree (LLB), and then further training. While universities don't stipulate *specific* GCSE grades as an entry requirement for law degrees, they generally expect strong grades, typically including good passes in English and Maths, and often other subjects relevant to the course. The precise requirements vary greatly between universities.
A strong academic record throughout your education is essential for a successful application to a law degree. While GCSEs are a starting point, A-levels (or equivalent qualifications) and university performance are far more critical.