Best place to start is to choose on of the big 4 accountancy firms in which you would like to work for, depending on your A Level grades you may be able to get a sponsored place at university (if you choose to go down that route) and work for the company in your holidays and gain relevant experience (aswell as be paid). Once finished they may decide to keep you on in which you will complete a further two years and at the end you should come out as a chartered accountant. That is probably the quickest and cheapest route. You could also join on as a school leaver, but please keep in mind these courses are incredibly competitive and as a result you will need to perform very well in your A levels along with interviews (often 3) with written tests. If you go down this route it will usually take between 4 - 6 years till you are fully qualified.
Honestly getting a sponsored place is a fantastic opportunity, you effectively get paid to go to university. Keep in mind that you will need to get accepted into some of the big business universities such as Durham, Bath, Warwick for them to accept you.