James made bikes, tandems too I think. There was some discussion in the Veteran-Cycle Club's "News and Views" a year or so ago about James. There is a lot of knowledge available to members. It is possible that the chainrings have come from another bike but probably not.

For future reference: frameteam2003 is correct, it is a standard frame fittings kit and 1930s British tandems are notoriously difficult to identify.