Both, it depended on both preference and ability. They offered "double science" which consisted of core science and additional science and they also offered "triple science" which would leave you with separate GCSE's in biology, chemistry, and physics.
If you performed well in science in the lower years of school you were submitted to do triple science however if you felt uncomfortable with the workload you could choose to do double science. Those who weren't good at science in the lower years of school were submitted to do double science only. Although a few people did swap to triple science if they excelled.