Comeing from the KitCar side of things into the 4x4 scene we always had close contact with VOSA and I have to agree with simonr, a chassis is from the front to the back inclusive of any overhang from the axles. Basicly if you alter any part or even weld a patch over a hole in the chassis legally it needs to be retested and a MOT inspector can if he wants, refuse to test it and can report it to VOSA. At the end of the day they are closeing in on all 4x4's
Shhhhh, and through the back door from VOSA (whisper ) they are looking at making all 4x4's class7 MOT from 2012