British Rail returned to the idea of railbuses from the mid-1970s, and a prototype four‐wheel vehicle was developed jointly by British Leyland and the British Rail Research Division. Several single-car railbuses were built and tested, in co-operation with Leyland (hence the generic term for these vehicles as LEV (Leyland Experimental Vehicle) railbuses). The first three single-car prototypes were essentially Leyland National bus bodies mounted on a modified HSFV1 four-wheeled rail chassis.