Collosius,
Your timings are worst case scenario. You've already completed the two year GCSE courses. Therefore, if you pay for the exams yourself, you can go to the nearest examination centre and apply to resit at the next opportunity - there are at least two per year.
Hit the books on your own now, apply for the exams next June and you could very well start A-levels in September 2007.
Or, as you've already done the courses once, ask whether you could attach to the current second year for revision help with a view to re-sits next year. If they don't like that, ask whether you can join there current year one - you can't be that far behind... either way, you'll be at least a year ahead of your earlier calculations.
(Coming from someone who lost two years by pratting around before completing A-levels properly - it was only having my application to join the RN as an apprentice artificer rejected that forced me to go back and try again; result A, A, B followed by a degree at Durham)