QUOTE(andante_in_c @ Dec 16 2007, 06:27 PM)

Not impossible, but would it represent a huge challenge, I think. The work load in the sixth form increases greatly, and it takes a long time to put a diploma programme together, especially for piano.

Now, if you'll excuse me...
WOOP WOOP ** STANDARD RESPONSE ALERT ** STANDARD RESPONSE ALERT ** WOOP WOOP
The first thing to do is
READ THE SYLLABUS. Find out what a diploma actually involves - both the AB and TG diplomata are about more than just playing a few pieces and scales; from memory the LCM ones do too.
I don't know what standard you're actually at, but it's a huge leap from Grade VIII to associate diploma level, so to bridge the gap in a year you'd either have to be well beyond Grade VIII next winter, or be prepared to put in an awful lot of effort during the year, not only getting your performance up to standard, but preparing for all of the the bolt-ons that a diploma involves.