The mention of 'combined' science takes me back 20 years.
Of GCSE, started in 2010, Science, the majority of students should have the opportunity to get certificates in three sciences, by two pathways:
B1 + C1 + P1 + CAT = (core) Science
B2 + C2 + P2 + CAT = Additional Science
B3 + C3 + P3 + CAT = Further Additional Science
OR:
B1 + B2 + B3 + CAT = Biology
C1 + C2 + C3 + CAT = Chemistry
P1 + P2 + P3 + CAT = Physics
Both pathways cover exactly the same modules, teaching, controlled assessments and exams. Exactly.
They key difference is in the first pathway. The Further set of modules is optional, and the core exams can be taken and certified at the end of Y10. No decision on taking Further modules needs be taken until end of Y10/beginning Y11.
Whether a school goes for the first pathway (Science/Additional/Further) pathway, or the second (Biology, Chemistry, Physics), the students will be taught and will be learning separate sciences, ie they will know whether the lesson is biology, chemistry or physics, and will (hopefully) have a different, specialist teacher for each one. They will likely be timetabled to have all three sciences in the each week. It is perfectly truthful for a school to say that they teach separate sciences to all pupils, regardless of how they administer the exams.