C & D1 Driving licenses...

Hello! I have a full B driving license. I need to obtain C & D1 as well. Is there a seperate theory test for these? Or is it just a matter of doing the tests?

Thanks.

From citizens information:

If you wish to apply for a truck driving licence, you must sit the category C driver theory test. This will entitle you to apply for a provisional driving licnece in categories C1 or C. If you wish to apply for a bus driving licence (category D), you must complete the category D theory test.

(and yes, the mis-spelling of "licence" is on the website!)

Cheers for that.