Yes. You will need to take a theory test if you want a licence for a new category of vehicle, for example, if you have a car licence and you want a bus licence you will need to take a theory test.

To upgrade within a vehicle category you will not normally have to sit the test, for example, if you have a Category C licence (Class II) (rigid body lorry) and you want a C+E licence (Class I) (articulated lorry) you will not have to take a theory test. You will however have to take the relevant practical test.

Anyone with sub-categories C1 and D1 entitlement who obtained those categories when they passed their car test and wants to upgrade to a C or D licence will have to obtain the correct provisional entitlement and pass a theory test.