There isn't a specific set of GCSEs universally required to become a social worker. The entry requirements vary depending on the university and the specific social work degree program. However, most universities will expect you to have at least 5 GCSEs at grade C/4 or above (or equivalent), including English Language and Maths. Some may require more GCSEs or higher grades.
It's crucial to check the specific entry requirements for each university's social work degree program you're interested in applying to, as these will be detailed on their websites. Don't rely on general advice – always refer to the official university information.