BSA had a long-standing relationship with the British Government dating back to the Second World War, when they had supplied the forces with dispatch riders' bikes in the shape of the M20. Post-war the military had an excess of machinery for its peacetime needs, and so the M20 continued in use for many years. Eventually, it was decided that a more up-to-date replacement would be required, and the government turned once again to BSA. Having been introduced in 1961, and derived from the unit-construction C15, the B40 overhead valve 350 engine was deemed both powerful and compact enough to fit the bill. Modifications would obviously be needed to fit the military specification, and the frame from the competition C15 variants was used, together with double-damped forks. Trials gears were utilised, and an engine oil filter was fitted. Some were fitted with a military-spec carburettor, whilst others used the Amal mk1 Concentric. Although the majority of WD B40s date from 1967, this one displays a military plate on the steering head with the date February 1970.
Purchased by the deceased owner in 1989, ECK 666Y appears to have had little use since that time, and displays a mileage of 6,995 on the odometer. The latest MoT on file expired in September 1998. Having been standing since that time, it will now require some degree of re-commissioning. Documentation accompanying the B40 comprises a current V5C, and 3 expired MoT certificates.