According to the book "Action Stations Revisited" vol. 2..........
On 1 February 1946 Dakotas of the European Division BOAC (alias BEA) started operating civilian passenger services from Northolt to Paris, Brussels and Amsterdam. Northolt was lent by the Air Ministry to the Ministry of Civil Aviation from 4 February 1946. Civilian flying increased as foreign airlines started services into Northolt. Among them were Alitalia, ABA Swedish airlines, Aer Lingus, Czech Airlines, Danish Airlines, LOT, DNL and Swissair mostly using DC-3/Dakotas, later C-54 Skymasters. Autumn 1946 saw the introduction of Vikings by BEA. RAF Dakotas had continued to operate services.
By 1952 most airlines were using Heathrow and, in October 1954, Northolt returned to RAF control.