[2] For most of that period, after the introduction of 'Learner Laws' in 1961, a 250 cc was the largest capacity solo machine that a learner could ride unaccompanied when displaying L-plates in the United Kingdom.

[2] Producing only 15 bhp (11 kW), the C15's lack of power meant that it was hard for the BSA to compete with the more sophisticated Japanese motorcycles (such as the Honda C71 and CB72) which began arriving in the UK in the 1960s.

[3] The C11 engine had an iron barrel and alloy head with overhead valves operated by pushrods which ran in a separate tube to fully enclosed rockers.

The frame was single loop with twin rails under the engine and pivoted fork rear suspension, and both wheels were 17 inch with full width cast iron hubs.

[3] Initially, the contact breaker housing protruded at the rear of the cylinder above the gearbox, but was later relocated to the right-side crankcase, accessed via a circular plate.

The BSA C15T was a trials version with a higher clearance frame fitted with a reinforced plate, special gear ratios suited to off-road use, a 20" front wheel in the UK and a high level exhaust pipe.

The first series competition frame with single down tube suffered rear tyre clearance problems in heavy mud.

The scrambler C15 shared the same frame as the trials (designated with a C suffix), had a larger exhaust valve, higher compression ratio and modified camshaft for more power.