Hi Graham,
I used Phil Croucher at capt.gs - see
http://capt.gs/courses.html for courses and prices
I was originally going to do the CPL but then decided as there wasn't that much difference in cost (other than a bit more groundschool) I'd do the ATPL. Well the CPL course is aimed at about 250 hours of home study and the ATPL about 650 hours of home study so there does seem to be a lot more in the ATPL, and when we were doing some groundschool with a mix of CPL and ATPL there were lots of areas where Phil would say "this bit isn't in CPL".
This blog put me on to CAPT and gives a good write up so I won't repeat it here.
The ATPL took me just under 9 months of study (whilst working full time), but I tend to be away quite a bit (as people who know me will see) so that included a number of breaks for holidays, weekends and a CRI course. Spent quite a bit of time doing question banks to help me understand my 'weak' areas to focus on.
I'd say CAPT is ideal for the person who wants the minimum amount of 'compulsory on site' training and is more focussed at people who are existing pilots with knowledge who want to be guided/supported in their self study than a number of the other providers I looked at (which suited me fine).
There was a chap on my groundschool who was a semi retired IT consultant who had is FI (but only for NPPL) and was doing the CPL theory for his PPL. I got the impression that at a CPL level he didn't find it too difficult if he knew enough to teach the subects to PPL level.
Mrs derekf is now doing her CBIR theory through them as well!
In hindsight, it would have been a lot simpler to go for the CPL TK than the ATPL TK, but I've never been one to dodge a bit of a challenge!
Hope that helps...