NLP645 was one of 65 AEC Regal IV's with Park Royal C37C body, new in 1953 and operated by London Transport on behalf of British European Airways. By the time this photo was taken, it was being used by Yardleys (perfume manufacturers) in Basildon for staff transport.
The body was built to London Transport design on a deck and a half principle with the rear half of the seats raised above a large luggage compartment. They were used to transport passengers between BEA's London terminal at Cromwell Road (now a supermarket) and Heathrow Airport.

Photo taken by Chris Stewart, 1977, Basildon