BOAC also operated from 1946 to 1949 flights between Southampton and Rose Bay in Sydney Australia using (I believe Sunderland) flying boats. This was perhaps the worlds first ‘codeshare’ route as it was operated in conjunction with Qantas who had a history of operating flying boats on intercontinental routes. Probably this was also the inception of the famous ‘kangaroo route’.
BOAC also operated flying boats from Southampton to Hong Kong. The attached image was taken from the ferry pier at Kia Tak airport in 1949. Note the local HK Chinese air hostess.
Indeed a ‘Serious long-haul airline network outside London’ as they also operated to other destinations including Singapore, South Africa, Canada and the USA using a variety of flying boat models.
