Hi motoxman, welcome to RR.
I'm not sure about GS for other branches as I deal with engineer officer recruiting. For EO, you need maths and physics A-level + 5 GCSEs (including maths, english language and physics), so if you've got those as well as GS it shouldn't be a problem. You need 180 UCAS points.
Ninja or Supermario, the AFCO fonts of knowledge, will no doubt be along soon and are better paced to answer your question.
Still deciding on the branch, but it won't be EO as I don't have physics. Unfortunately I only did two A Levels achieving a C in each plus general studies at a D. So if they count GS I will have 220 UCAS points, otherwise I'm buggered for now!
Having read through the post on here so far it looks like you should have no problems with the academic qualifications for Officer entry as Logistics or Warfare. You can use General studies to top up your UCAS points providing you have other "A" levels, so with Maths and Geography you will be OK.