Fleet Driver Assessment & Training Limited - Specialist Vocational Driver Training Vehicle and Trailer
D1+E (Minibus + Trailer)
Towing Practice, Training and Test
If you have already passed your minibus test (Category D1) and you need to tow a trailer greater than 750kgs then you will need to take a minibus and trailer test (Category D1+E). 
You do not need to apply for provisional licence as you automatically have provisional D1+E entitlement added onto your paper counterpart licence when you pass the D1 test. 
All that is required is Module 3 which is the practical test.