I'd use their own documentation against them. These documents were only updated in May this year.
V5C log book
It is a legal requirement that all UK registered vehicles are classified correctly on the V5C log book. All campervans, motor caravans and motorhomes fall into the DVLA category of ‘motor caravan’. If you have converted a van into a motor caravan then you must return the V5C to DVLA for body type amendment.
DVLA is required to record the details of vehicles for road safety and law enforcement. The body type information held on the vehicle record must describe what a vehicle actually looks like. This description, in addition to other distinguishing features, enables the police and other enforcement agencies to identify a particular vehicle. Therefore, the body type will not be changed unless the exterior of the vehicle actually appears to be a motor home.
Motor caravan minimum features
In order for a converted vehicle to qualify as a motor caravan it must have certain minimum features:
If the vehicle has all of these features present, permanently fixed and installed properly, then it is a legal requirement to have it reclassified as a motor caravan on the V5C.
- a door that provides access to the living accommodation
- a bed, which has a minimum length of 1800mm or 6 feet - this can be converted from seats used for other purposes during the day but must be permanently fixed within the body of the vehicle
- a water storage tank or container on, or in, the vehicle
- a seating and dining area, permanently attached to the vehicle - the table may be detachable but must have some permanent means of attachment to the vehicle. It is not good enough to have a loose table
- a permanently fixed means of storage, a cupboard, locker or wardrobe
- a permanently fixed cooking facility within the vehicle, powered by gas or electricity
- at least one window on the side of the accommodation
I am sorry but it does appear that people are still conveniently omitting the body type requirement ( Not that it is defined above), this is what is being amended on the V5 not the interior fixtures and fittings. Everyone appears to be reading the internal requirements in isolation whereas the body type requirement needs to be satisfied first. ( I am not in agreement with the way that it is set out but the 1st requirement is clearly stated to be the body type) If you throw this document back at the DVLA they will just point you to the body/exterior change every time.
I spent quite a few years dealing with directions like these as a Civil Servant so it may be easier for me to digest the offending document but it must be plain for all to see that the body type requirement must be satisfied first. ( I am all for the blanket amendment of the V5 with the internal changes defining a motor caravan as it used to be but you cannot argue against what the current requirements are).