I believe CATS (Cranfield Aviation Training) is divided into 3 modules, but that's the most I've ever seen.
I'd stick with one school and the study materials from that school. The courses are designed by folks who know what they are doing!
I have heard excellent things about Bristol, though I must say I have heard some great things about CATS too.
London Met also do ATPL ground school-keep an eye on the advertisement banners on this site.
You could also do a residential course through one of these providers, or somewhere like Oxford/Cabair also offer courses, if somewhat expensive.
B