Yeah, thanks - that's an understandable reason for doing the IR last. Really I was just figuring it all out for interest due to the number of possible routes. I understand the value of consistency in professional training (I don't count the ATPL's as necessarily within this as Bristol Ground School are obviously successful as an independent entity from any flight training organisations that also offer ATPL study).
Looking at Bristol Flying Centres prices, it's actually slightly cheaper (£1k) to do the IR before CPL (on weak assumption of min hours), though I think flyhighspeed's reasoning carries through, particularly in employers preference for currency and this is therefore probably false economy as it's a much more expensive rating to keep current (keeping in mind that the job market is unlikely to improve for some time).
Doing a MECPL first is therefore probably the best compromise for me, then I'll revalidate the ME rating during the IR training at a later date (and before my 3yrs ATPL credits are up!!). Hope this is of use to others researching in future.