Thankyou Skipness and Flightrider. I suspected that the looming BA branding with Manx Airlines (Europe) might have prompted a change of airline and basing the aircraft at LBA, within what you describe as LBA territory. Ironically, just over a year later, MXE (as BA Express) had become established at LBA in their own right as they based two J31s to operate the former Knight Air routes. In another year's time, the 31s were replaced with 41s and eventually became four in number. At a similar time, the ATPs were returned to MXE and the ex-Business Air Saabs picked up the LBA Scottish routes as BM Commuter. The J41, MAJA, stayed with British Midland for a little longer before too returning to Manx and being repainted in the classic Manx Airlines livery.
As a sidenote, although MANL and MAUD were the de facto British Midland ATPs, it was occasionally necessary to send a replacement aircraft, usually because the incumbents were tech. More often than not, BRLY and BUUP did the honours but, one time, a MXE ATP in full BA Landor livery turned up to operate the British Midland routes! I don't recall this happening again but I'd be interested to know if Sir Bishop heard about it!