All exams ever taken are supposed to be declared on UCAS, so technically at least he would have to declare all resits and original results, although I'm not really sure what would happen if he didn't. The resits would show as resits in any case due to the date they were sat.
For physics and biology he would need to resit the practical elements which could be tricky to organise and time consuming and there is a fair bit of revision work for the exams for those subjects too - I would say not worth it.
For the English Language there is the possibility of a November resit, but I think 60% of the marks are on the controlled assessments (it is probably slightly less than this now the speaking and listening has been taken out, but still a high proportion) which would be a massive pain to re-do, again, not worth it. Resitting the exam though can be done without much/any preparation. One of my dc did this 2 years ago (when the school recommended it to those with a narrow miss who they felt had been robbed, as the resit was offered free that year due to the hoo ha over the grades). Even though it was mainly the CA where the expected marks had been lost (she didn't redo this) and she did no extra preparation for the exam, the resit result came back a percent or two higher which was enough to shift the overall B grade to an A. As truth says, the high weighting of the CA means an exam resit realistically can't raise the result from a B to an A*, but it can nudge it up to an A.
Whether it was worth it or not I don't know. Only the very most competitive courses consider GCSEs in great detail - at the point she was still considering medicine, which at many places did need a GCSE A grade, but also a lot of them wouldn't accept resits either. Certainly, for what she has ended up doing the resit wasn't needed (they told her this at interview).
Most courses will be far more impressed by high AS and A level grades, so arguably, putting these results behind him, trying to learn from any mistakes made (did complacency after high mock results play a part?) and
working towards the best possible A level grades would be his best option.