Depending on what kind of qualification you want I know Bangor University offers a herpetology module in the third year of studying zoology and conservation and the person who teaches it is a very good herpetologist with lots of published works (some i've tried to read myself but they're a bit above my level).
I'm thinking of doing the Proteus course (mentioned above) myself so if I do it before you or find anyone who has done it i'll give you an overview, but the description on the site sounds as though the course is worth the money.
Regards, Matt.