Reintroduced post-war in 1946, the M21 continued for many years as a sidecar bike in the BSA range. Used occasionally as a solo machine, they were part of the range until 1963, by which time increasing prosperity and inexpensive four-wheelers had eroded the sidecar market. RSK 605 was purchased by the deceased owner in 1992, and was possibly unused from that date. It appears to have been fitted with an earlier engine at some time. Having been stored outside for a number of years, albeit beneath a tarpaulin, it will require restoration, and is sold strictly as viewed. Documentation accompanying the M21 comprises a current V5C.