As it appears to have only one exhaust port on the right hand side, the engine would be a 148cc Mk15C. This appeared in 1934 as a slightly cheaper version of the Mk12C introduced in 1932 so unless the original 12C cylinder had problems and been replaced by a 15C (they're interchangeable) the the bike has to date from at least 1934.
It can't be a Coventry Eagle as they had a very distinctive pressed steel frame.
Villiers dominated the lightweight market at this time and a large number of manufacturers included a Villiers powered lightweight in their range regardless of what else they made. Sometimes they can be very difficult to identify. It makes an interesting challenge.
Cheers, Bob
