The type of license you need to drive a motorhome depends on the weight of the vehicle and when you obtained your driving licence.
If you passed your driving test before 1st January 1997, then you will be able to drive the vast majority of motorhomes without a special license. However, if you passed after 1st January 1997, you can only drive vehicles that weigh up to 3,500kg with a trailer weighing a maximum of 750kg.
If your license is not valid to drive your motorhome, then you need to obtain an entry-level HGV license.