light goods vehicle vs diesel car?

[aclivity]

Simple question - what is the difference between a light goods vehicle and a diesel car, when the car in question is a 7 seat LWB landrover Defender?

[All that jazz]

Cosmetically and mechanically, often nothing, but light goods vehicles often have a different taxation class and depending on the GVW, possibly different speed limits.

[aclivity]

taxation comes out lower - £220 per year. Just wondering about the speed restrictions?