@Mick
This may help you understand
@Bav 's &
@Salty Spuds comments.
In 2019 after conversion, I tried to get my panel van reclassified as a motor home / motor caravan, but it came back as a "panel van with windows" even after submitting a full campervan build report & loads of photos, both internal & external.
I then asked for clarification re speed limits and this was the reply:
Re: "Van with windows" speed limits / clarification
Thank you for your online enquiry made to the Department for Transport regarding the speed limit of your vehicle. It has been passed to the Driver and Vehicle Licensing Agency (DVLA) and I have been asked to reply. The national speed limit for different categories of road vehicles depends on how the vehicle is configured for use on the road. That generally means whether the vehicle is designed primarily for the carriage of passengers or goods. The "body type" field on the DVLA vehicle record should not be used to determine a vehicle's speed limit as this is used purely to describe a vehicles external appearance in traffic, to assist the police and other enforcement agencies. A vehicle with "van with side windows" body type does not necessary mean it is restricted to speed limits of a goods vehicle. Provided you are satisfied the vehicle meets the internal requirements to be recognised as a motor caravan and any alterations made to the vehicle do not compromise its safety, then it should be treated as having a speed limit of a motor home or motor caravan in the guidance found here: www.gov.uk/speed-limits
Mr Salty Spuds is correct in saying it's a big can of worms & it's fully understandable why people misunderstand the rules.