As a rule British adult airguns tend to turn up in .22 calibre more frequently than .177. However the old BSA under levers don't seem to follow the same rule.
I know that the reason for this generally is that the old (pre 1968) airgun power limit was done on muzzle velocity rather than energy, which gave 22's an edge, but with the BSAs would the fact that thousands of them were sold locally for bell target shooting account for the higher incidence of .177's?