If you want to go to university and study at degree level, then yes, I would recommend A Levels. Aside from the fact that most of the traditional universities prefer these qualifications (regardless of what the government may say), degree-level study is a big jump from GCSE and even A Level and you really need a good grounding in the basics of a subject before studying it in that much depth. Many universities now go as far as to differentiate between A Level subjects they class as 'easier' and 'harder' and will specify which subjects and which grades you should aim for in order to get onto a specific course.
I didn't get very good grades (and didn't choose core subjects) at A Level the first time around and they have been useless. I could have done better at GCSE's too, but at 20, felt too old to go back that far. I studied and passed A Level English Language (and a couple of other 'soft' subjects) and did not use any of the information I studied in GCSE English - it had been 5 years since highschool anyway, so I wouldn't have remembered anything.
If you want to prepare for an A Level then spend a month or so going over a GCSE revision book in that subject to cover the basics. Many A levels are not taught at GCSE level as part of the main curriculum in schools (law, economics, business studies, geology, history of art... for example), so the subject would be completely new to most students, regardless of GCSE grades.
I'm nearly 24 and now taking Maths and Physics A Level through ICS, whilst working full time to save for university (don't want the scary debts). I think a lot of the bad rep that ICS and other home-study providers get is down to the fact that people expect the level of support to be like that of college/sixth form and it is more like degree level - where you are given the basics and told to get on with it. My company sent me off to a near by uni to take a short business course and it was very much the attitude that students would teach themselves for the most part, with some help/guidance from the tutor. We had a few interesting talks and lectures a week and a general tutor to ask for help (if we could find them), but we worked it out ourselves. At least for A Level subjects you can buy compact revision guides for all the content!
If you are planning on going to uni then this will be a good habit to get into, however tough it may seem to begin with. All of my friends went on to study at good universities, so I have seen the workload for myself and heard all of their stories over the years. Some of them studied A Levels at a private sixth form and were basically spoon-fed the course content by their teachers. Going on to degree level was a massive shock to them!
If you are studying with ICS then make sure the exam board used is one of the well-known ones (AQA, Edexcel, OCR..) and get hold of the syllabus yourself along with a good revision book and supporting textbooks. We were given the main textbook in college, but still had to buy extra ones ourselves and ICS is the same. There is a lot of background reading/studying to do that you organise yourself, but then there would be at a college/uni. When I took my first lot of A Levels, it was suggested that we do about 4 hours a week of 'own study'. There are many revision books out there that cover everything needed (find out which ones your local sixth forms/colleges use and find one with a format you like). You just need to do a bit of research before you begin - not rocket science!
Yes, you will need to arrange to sit exams with exam centres (and the same for practical work if you take science, for example), but you can arrange this well in advance so to avoid last minute panic and can sometimes sit exams with students at a local college or sixth form for a cheaper price. I am sitting mine in London as none of the local colleges or schools accept external/private students - so I'll jump on the train, take the exam and then spend the afternoon/evening doing 'touristy stuff' to calm post-exam nerves! No, ICS do not arrange everything for you and tell you when to turn up, where to go, where to sit, etc but it really isn't all that difficult to arrange. If you can't cope with ringing up an exam centre or getting on a train, then you probably shouldn't be doing a home-study course. I know that sounds cold, but it's the truth. I found it straightforward enough.
I think it boils down to how self-motivated and independant you are and whether you need someone else there holding your hand. There seems to be (from my experience anyway) a very close knit and supportive student community at ICS, which makes up for the lack of face-to-face teacher support. I have not had any problems with the tutors so far (it is early days), but then I don't rely on them to expain everything to me. I just find the information myself from the vast amount of resources available online, at the library, through internet lectures, etc.
With ICS, you are really paying for:
1. A basic subject tutor to set and mark assignments for extra homework and ask questions if you really can't find the answers yourself.
2. A student support network (the main reason I chose to sign up with ICS and not completely teach myself). Studying at home does get lonely and boring at times and it helps having 'peer pressure' to keep you going and someone to talk to who is going through the same thing. You can arrange study groups/partners (online, on the phone or in real life if they live close enough) and people seem to be far more motivated than the students were in college as they HAVE to focus and get things done themselves. When I did A Levels at my old college, most kids found it hard enough just to bother turning up for the lessons and paying attention!
and 3. A basic outline of the syllabus to follow throughout the course along with some extra materials and books.
They are really an organisation to help students who already feel comfortable enough to study at home. Those who panic at the thought of having to travel to an exam will find it a big jump completely moving away to study at university (as many have to) and probably should spend an extra couple of years in a classroom before taking the plunge at degree level.
I've tried to be honest, even if it doesn't sound 'nice'! Either way, best of luck with whatever route you decide on and it's great that you are choosing to advance your education.