I know the Grade's range for Grade 1 - 8 (at eight you're consider a "professional" I believe). But that's about all I'm able to really tell you.

I've done a search in Google, have take a look at this link below and browse around a little, hopefully it should give you all the information you need - it seem's pretty informative from what I've briefly read, so it should at least give you an idea of where to start looking if nothing else.

http://www.registryofguitartutors.co.uk/exams/electric/electric_guitar.htm

They also do Bass and Classical guitar, so if you're not after electric, you should be able to find what you want.

Hope that's of some use,

Regards,
Chris.