Can I drive a dropside van on a standard licence?

Yes, you can drive a dropside van with a standard car licence if the total GVW is up to 3.5 tonnes. Anything over 3.5 tonnes and up to 7.5 tonnes will require a Category C1 licence. 

However, if you passed your driving test before 1997, you'll have automatic grandfather rights, and you'll be able to drive vehicles up to 7.5 tonnes (Category C1 Licence).