When i suggested this previously i was told that its not possible due to some sort of agreement that doesnt allow Cityflyer to operate into LHR or LGW
cs - I think the agreement you are reffering to is "scope" This prevents any subsidiary or franchise operation from using the same type of aircraft as mainline, or with more than 100 pax seats, Hence EMB 195's. Remember cityflyer was originally a LGW operation.