Weren't the VC10 C1 pilots all Sqn Ldrs as well to stop them defecting to the darkside where the pay was greater for those under Sqn Ldr rank, and that only ceased when the Civilian world got rid of them and sold them to the RAF, then you started getting lower ranks flying them.
Not quite true. A lot of Transport Command captains were very senior flight lieutenants who performed their duties away from base and out of sight of their CO. They had virtually no chance of getting their scraper. By comparision fighter command pilots on tight knit squadrons, always in close contact with their boss,had a very good chance of promotion ay an early age. After lengthy negotiations the bean counters agreed to a fixed number of captains on the strategic transport fleet holding the rank of acting squadron leader while in post. The C in C Transport Command, AM Sir Thomas Pricket, allocated all the acting Sqn Ldr posts to 10 and 216 sqn. The acting scraper became known as the Prickett ring of confidence. A lot of hairy old Britannia and Belfast captains were not amused.