Genghis,
As per my earlier post, it's 36 months from the date of last your ATPL pass to obtain an IR. If not obtained within that time then your ATPL theory will lapse.
If you do decide to do the IR within the timescale then your ATPL passes will remain valid for 7 years thereafter or alternitavely, as kong as your IR is current.
J - As for groundschool, there are plenty places to choose from for ATPL theory, but not CPL theory. Somebody may correct me here but I think only AFT at Coventry do the CPL. You could always check the CAA website though and get a list of groundschool providers. I did my ATPL theory at Glasgow(College of Nautical studies) but turning the clock back I would probably go to Bristol. They have a great reputation and their feedback is spot on!