there is a grey area around smaller vans i drive a fleet van for british gas and we had an issue in fife where one of our engineers was stopped and fined, he argued it was a car derived van, we went to fife police HQ in glenrothes with our fleet manager and spoke to the man in charge of traffic, he explained the "panel van " rule but couldnt define a panel van vs car derived to an exact point, it ended with kangoo/berlingo/caddy as car derived and transit /vivaro as panel vans, which in my mind was clear, the one that caused the stink was ford transit connect which was really inbetween, the company has now decided the whole fleet has to be treated as panel vans and use the lower limits, our entire fleet now has limiters,
as for crew cabs etc its something to do with weight limits like the mot, my 110 van side states 2895kgs or similar but some say 3500kgs making them class seven