Hi,
There are no specific IR exams, certainly that I know of.
First things first, go to the CAA Website and download a copy of LASOR’s. As far as flight training and licensing goes, it’s the bible.
If you want to hold and ATPL (be a captain on a commercial airliner), then you must do the 14 ATPL theory exams as you say, possibly by distance learning. If you do not, say you wish to be a career instructor, then I understand the CPL examination subjects will suffice.
I think AFT in Coventry are the only school which does the CPL only syllabus. Quite happy to be corrected though!
The theory part of the ATPL’s can be done in a little as 6 months, I have heard!! They took me about 15 months, but I was working and hour building at the same time.
There are timescale limits, which triggered by the first exam sitting, but I can’t recall what they are.
Have a read of LASOR’s – it answers all your questions.
Best of luck with the training.