Took an engine block up to a mates ready for a scrap run next , came out of his yard after about half a mile 'bong' off rd height 30 mph max comes up , so i stopped , back end was indeed up in the air , front end was normal , what the hell is going on ???

No idea really, but maybe it shoved more air into the rear bags to keep the car level with the engine block in, so when you removed it, the back was pushed higher......but.....the car should deal with the weight being removed, and then drop the air in the rear bags.

Only a thought.... 2011 Range Rover Vogue SE 4.4 TDV8

Previous cars :
2003 Range Rover Vogue TD6
1999 Discovery Td5 ES
1995 BMW M5 3.8 6 speed
1992 Range Rover 3.9 Efi Vogue
1992 BMW M5 3.8
1988 BMW 735i SE
1989 Ford Sierra XR4x4 2.9i
1981 Ford Fiesta Supersport

That makes sense pal, guess it hasnt registered the fact the weight has been temoved ?

Right , plugged in with Delphi and got a canbus fault and front right height sensor / left rear height sensor , i deleted the codes and it seems ok but it wont go to off rd height but i guess the pump is getting warm