In the early and mid-fifties, when I started in this aviation business, I worked for Skyways of London at Bovingdon and Stansted. At Bovingdon we got the 10 Hermes from BOAC and converted them for trooping and they did not have military serials, although at the same time some of Airworks Hermes at Blackbushe did.
There was a connection between Skyways and Lancashire Aircraft Corporation so aircraft ownership was a bit mixed.
When the Bovingdon operation closed, after the 10 Hermes had been converted, I transfered to Stansted and saw several Yorks with military markings and the crews wore RAF/VR uniforms when flying them. I thought that the aircraft used their old military serials when flying these trips but I could be wrong at this late date!! I seem to remember numbers like MW???
There were also several Yorks on the dump/spares/awaiting conversion pile that had military marking and a civil registration hastily painted on. These were ferry markings to get them to Stansted from the RAF, MU's.
At the time the Yorks were busy with Middle East and Far East military contracts. The Hermes were used for Singapore trooper flights and to Cyprus. When the Hermes came on line the York flights were coming to an end.