From RAC website : Year ==> 1960 , Capacity ==> 2451 cc.
Confirmed by DVLA :
The vehicle details for 2868 AD are:
Date of Liability 01 07 2007
Date of First Registration 16 05 1960
Year of Manufacture 1960
Cylinder Capacity (cc) 2451CC
CO2 Emissions Not Available
Fuel Type Petrol
Vehicle Colour BLUE
EDIT - Extra pic showing the absence of vent windows (appeared with the 4th series?):
The thumbnail shows, indeed, the absence of the quarterlights on the front doors that would identify it as one of the cars from the last 6th series ( 1957 ). I think this can be a 1954 4th series car by the push-button door handles, the black steering wheel and the absence of a chrome trim on the bonnet ( introduced in the 1956 5th series ). It also seems to have a tinted windscreen and only the 4th series had tinted glasses. The right door window doesn't seem to be tinted but it was perhaps replaced at some point.