As someone who worked for Southdown between '62 and '66, I remember both the Portsmouth and Brighton agreements. Part of my training was as a conductor in Portsmouth. The agreement meant we could pick up short distance passengers throughout the city on the country services. On those coming up Commercial Road meant you got a real bashing, even in the off peak. In order to balance out the mileage, Portsmouth Corporation buses used to be used on Southdown services. I don't remember any year when Southdown buses operated on Corporation services, nor any similar arrangements in Brighton. Although the Brighton scheme, BATS as it was known, was supposed to eliminate wasteful competition, Southdown maintained a circuitous service to Woodingdean competing with a direct service operated by Brighton Corporation. The Southdown service was very little used and when the company ran into difficulties with staff shortages in 1965, journeys on the service were not operated. At it's worst, the advertised half-hourly service didn't run at all between morning and evening peaks. Occasionally, London coach drivers, on lay overs in Brighton, would operate a couple of journeys during the midday period.