The categories of vehicles are set out in the EU Driving Licences Directives which form the framework for our national legislation. Small commercial vehicles fall into either Category B or C depending on the weight of the vehicle. Category B covers vehicles with a Maximum Authorised Mass (MAM) not exceeding 3,500kg. This is the average car category. Category C covers vehicles, other than buses, with a MAM exceeding 3,500kg and can be combined with a trailer where the MAM of the trailer is no greater than 750kg. Category CE covers Category C vehicles where the trailer is greater than 750kg. Category C1 covers Category C vehicles with a MAM not exceeding 7,500kg and can be combined with a trailer where the MAM of the trailer is no greater than 750kg. Category C1E covers Category C1 vehicles where the trailer is greater than 750kg but the combined MAM of the vehicle and trailer does not exceed 12,000kg.
Vehicle are grouped into categories as it is not possible to have categories for every individual type of vehicle.
Separately you may be interested to know that one of the proposals in the Mobility Package currently being finalised at European level is to bring vehicles with a permissible laden mass in excess of 2.4 tonne (i.e. light commercial vehicles) into scope for road transport operator licensing for international road transport. Currently only vehicles with a permissible laden mass in excess of 3.5 tonne are licensed for international road transport of goods for hire or reward.