I'm thinking of going back to uni and I've done Access to HE, and I'm currently studying A Level Maths and Further Maths alongside a part time job.
I've heard people got into UCL, Exeter, Bristol, Nottingham, and York with Access, so it's good. The thing you need to be wary of is the unit requirements the particular degree program will ask for. Some courses don't accept Access diplomas even if the uni does (usually English unis). Some courses need you to have 15-30 credits in a particular topic before going into the course. As far as I know, Imperial doesn't accept Access at the moment. The cost for Access can be from £1500 to £3500
In terms of A Levels, if you have done a Level 3 qualification before, Student Finance tend not to fund you on your second attempt (your funding for Access should be offered so long you go to uni very soon after the course). In terms of cost, you can either try to self study and apply for the exams, or go with a college offline (if local) or online. 6th form colleges tend not to aceept people over 19. I'm currently with an online college. A single A Level with colleges I've seen can cost from £300 to £800, but you might want to check with the colleges you want to attend.
I don't work in the IT industry, but I have a cousin who graduated with a CS degree from Liverpool and was only to able to get a high end job after a bit of experience. As far as I know, the industry cares more about your experience and what you have done than your degree (but you might want to get a second opinion). I'd focus more on the projects and work you can show off to people after uni really (most of which you can do now either for free or at low cost). A lot of the CS jobs I've seen will ask for a degree, even though I don't think the jobs need degrees. If disputed upon, you can try to look into the official qualifications, so people can't dispute the level of skill or knowledge you have (should be unncessary) e.g. Python and Oracle have their own programming qualifications for Python and Java. CompTIA has a set of qualifications that cost less than £1000, but I am not sure if they are that widely accepted in the industry. Microsoft tend to offer their own qualifications for IT, if you want to specialise in Microsoft related products. Google also have their own courses (some you just need to pay the exam fees for).