Single award science won't be an issue other than perhaps a few topics in chemistry that might be applicable. So called "triple science" is just students taking all three single award sciences. Double award sciences actually covers less over the three topics than each single award, and since unless your school has a different structure double award sciences is the only assumed prior knowledge for A-level sciences (and you won't need any of the material from GCSE Biology and very little form GCSE Chemistry for A-level Physics), it shouldn't make any difference.
I would note that computer science courses in the UK (and related degrees in computing, IT, software engineering, etc) normally do not require any prior programming experience or an A-level in CS or a similar subject. Many if not most applicants to those degrees (except for the few that do require that subject, which are very few and far between - Cardiff is the only notable uni I can think of that requires it) have no prior experience in the subject. Normally the only required subject is A-level Maths (with A-level FM being heavily preferred by the likes of Oxbridge, Edinburgh, Imperial, Warwick, etc).
In actual fact A-level Physics would give you more options than an A-level in a computing subject, as A-level Physics is normally required (along with A-level Maths) for almost all engineering degrees (including electronic/information/computer systems engineering, as opposed to CS which does not require A-level Physics), as well as physics degrees. A-level Physics is also generally the more relevant/useful subject for most mathematics degrees in the UK (which usually include some applied maths content that builds on the kinds of topics done in A-level Physics, although the knowledge isn't presupposed).