Mark, it is a common misconception that the taxation class defines the speed limit. Sorry, but this is categorially
WRONG. I am putting that in bold to emphasis it.
If you have a vehicle that is a Motor Caravan and it is under 3.05t ULW, you have car speed rights. No ambiguity, it is black and white. Taxation class makes no difference. If you are referring to the N or M entries, there are countless vehicles that have neither entry (two of my last three vans had no entry there).
Speed Limits in different countries than the UK - a different matter. We are talking about the UK when it comes to speed limits.
https://www.gov.uk/speed-limits
And the key text ...
"You must not drive faster than the speed limit for the type of road and your type of vehicle "
Note "TYPE OF VEHICLE" and not "TAXATION CLASS" - and it goes on to list the type of vehicles and their permitted speeds.
Automated systems may well be wrong but it is a matter of challenging if they come up with the wrong info. There is always the right of redress if incorrectly charged and if you are a Motor Caravan under 3.05t ULW and get "flashed" when travelling at permitted car speeds, you challenge and you win.
Now Housing Estate Covenants ... if you have a jobsworth saying "no commercials overnight" and your vehicle is a "Van/Side Windows" then you will have to defend your stance and could end up costing solicitor fees if contesting and likely lose anyway. If it is a "Motor Caravan" then it is clearly not a Commercial and you can tell them to pee off as you have proof (the V5C) it is not. The whole onus of proof is reversed.
If a Car Park says "no commercials" then you CAN park your Motor Caravan there obviously as it is not a commercial vehicle. However, some car parks says "no motor caravans overnight" so in that case your converted "Van/Side Windows" is better
. A local car park to me bars me regardless as their sign says "no vehicles over 3.5t". C'est la vie.
Ferries. Now this is a weird one. I have seen posts on the VW Forum that say some companies have charged them a surcharge over a van BECAUSE they are a Motor Caravan. Other Ferries it is a saving. Some use a database, some go by what a vehicle looks like.
Insurance .... plenty of companies will not entertain covering a commercial but will cover a Motor Caravan. If you have a multi-car policy, then they will not accept a van to be added (ANY van) but will allow a Motor Caravan to be added. Obviously plenty of insurance companies will provide cover, but it does means the options are more limited if not a Motor Caravan on a V5 (you did ask what difference it could make!).
I'll give you another one for the list from the recent past .... My old T4 was a Panel Van on the V5C and was the 800 Special model (so was 2.46t GVW). I could not drive into the LEZ when I bought the vehicle without paying a £100/day fee, but once I had it reclassifed as a Motor Caravan in 2015 I could enter with no problem and no cost - same vehicle, same engine, different body type. The Dartford Bridge uses the same database, so the cost of crossing that in the T4 as a Motor Caravan would be a lot less.
Makes Sense? Not at all, but that is a different discussion entirely.