Thanks So much Lapis - this is really useful information which I will investigate! It's an option which I hadn't even thought of! I have put a question on the Gloucestershire forum.
I live in Wiltshire but north of the M4, twenty or so miles from Trowbridge. Depending on the commute you want to work/school you could look at basing yourself around Malmesbury. A good comprehensive secondary school in the town or the alternative of an organised bus to the two grammar schools in Stroud (which accept out of county applications).
Have a look at the Gloucestershire forum, I have been a long time lurker and occassional poster there (my eldest is in sixth form) but my old log in details have escaped me at this moment!
Lapis (formerly known as ?)