As far As I can work out an Explorer is a 'Road Recovery Vehicle' described as:
Special types-road recovery vehicles
A road recovery vehicle is a vehicle that is; a locomotive; an N3 motor vehicle; or a combination of an N3 motor vehicle and an O4 trailer; which is
A specially designed and constructed vehicle for the recovery of disabled road vehicles, fitted with a crane, winch or lifting system for recovering another vehicle.
Heavy Locomotive, described as:
Mechanically propelled vehicle itself not constructed to carry load other than equipment for propulsion, loose tools and loose equipment, UW exceeding 11,690 kg.
They are not designed to carry goods, so are not HGVs, as locomotives they can tow up to 3 trailers.
Unless anyone knows different of course