You need an immobiliser of some kind. It can be mechanical (NOT operating on the brakes) or electrical.
from the latest IVA manual, section 13A:
http://www.businesslink.gov.uk/Transport_files/124_IVA_M1_Inspection_Manual_Version_1111.pdf
from the latest IVA manual, section 13A:
http://www.businesslink.gov.uk/Transport_files/124_IVA_M1_Inspection_Manual_Version_1111.pdf
IVA said:Check, in addition to the normal “ignition” switch, that the vehicle is permanently fitted with an anti-theft device or an electronic immobiliser that can be activated to prevent the vehicle being driven or moved under its own power.
A mechanical anti-theft device could be a steering lock or transmission lock. An electronic immobiliser can be activated by the ignition key (so would not be obvious) or could be separate - activated by a little fob type device
A manually operated battery master switch or a removable steering wheel would not be considered to be an anti theft device.