Rich,
I think you may be getting a little confused here! The ATPL is the license which you need to be captain of a multi-crew aircraft. In order to get that, you need a minimum of 1500 hours flying time, as well as lots of other requirements. No, you definitely don't need that first!
As Gonville says, "ATPLs" is often used colloquially to refer to the written exams. But I don't think that's what you mean, either.
If I understand you correctly, you are looking at schools where you can do the written exams (or the "ATPLs"), and the requirements for starting this course??? If I'm right, then the requirements are for a PPL - that's Private Pilots License, and it's a whole different beast to an ATPL!
The requirements for a PPL are a minimum of 45 hours training, but most people need around 50-60 hours. You need to budget around £6000-£7000 for this. If you want advice on the PPL, then post a question in the Private Flying forum, and you'll get answers there. (The Wannabes forum is for any part of your training which comes after you get your PPL.)
You mentioned doing things in a different order - I'm afraid this isn't an option. You must pass all the written exams before you can complete either of the next two phases of your training, which are a CPL and an IR. The only flexible bit is that you'll need to build some hours up before starting the CPL and IR training - and this can be done either before or after the written exams.
If I've mis-understood you, and this isn't what you're asking about, then please try to point us in the right direction and we'll have another go!
To answer your question about the medical, there is no fixed answer. The initial Class 1 has to be done at the CAA's offices, so they have a set price they charge. Renewals can be done by any appropriately authorised doctor, and each doctor can charge whatever they like. I renewed my Class 1 last week... I forget the exact amount that I paid, but I think it was around £80. (I paid by credit card, so it's not "real" money, which is why I can't remember the exact amount!
)
Good luck!
FFF
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