Trailer leg interlock system and procedure

The purpose of this invention is to protect a trailer by preventing accidental damage to articulated lorry trailers caused by the tractor unit pulling away when the trailer landing legs are not lowered as they should be when the trailer is to be parked. The invention provides an interlock system, the system comprising: a means that indicates the operational state of a trailer landing leg and whereby the system, responsive to the state of the trailer landing leg, constrains the release of the hitch coupling between the tractor unit and trailer, thereby preventing inadvertent release of the trailer if the trailer landing leg is not extended to its operative state. Extension may involve a lower leg 2 telescopically moving relative to an upper leg (1 see fig 1), revealing an aperture 3 and a key (7a see fig 3) for unlocking a padlock (10 see fig 7) for the coupling. A latch (6 see fig 3) for allowing leg retraction can only be operated when the key (7a) is inserted.