This will be enough for a student to enter less selective American colleges and universities. When you transfer from a U.S. Department of Education to a UK university, they will take the high school diploma as the GCSE equivalent and require you to obtain at least an acceptable grade at some A-levels. In recent years, the UK government has introduced a GCSE reform program, which includes a grading system that uses numbers (1) instead of letters (A-G).
In addition, GCSEs can be entry-level or higher; base documents have a maximum grade of C, while higher have an A*. The GCSE (General Certificate of Secondary Education) is the main end-of-school certificate in England, Wales and Northern Ireland (Scotland has an independent national grading system). For example, my school chose certain students to take their GCSE French or Spanish early, so they took the exams in Year 9, ALL students completed their ICT in Year 10, and those who studied GCSE languages early could take the A-Level of that subject early. Your GCSEs determine what sixth grade you go to and if you don't get a C or higher in mathematics and English, then you'll practically never get a good job.
When choosing certain subjects, such as Spanish and French, you had to have a minimum GCSE of grade C in those fields, but for subjects such as classical civilization it wasn't a problem if you didn't have a history like GCSE. I don't even think it has to be the test of the subject, only the ordinary SAT should be enough to be the general equivalent of GCSE.