AEC's Blue Triangle symbol [ AEC Ltd] is reproduced by kind permission of The British Commercial Vehicle Museum Trust.
The 1,000th Routemaster bus was handed over to London Transport in a formal ceremony held at AEC Southall Works on October 16th, 1961.  RM1000 was adopted as a showbus by staff at Croydon Garage, but was withdrawn in 1985.  Following a period in store, RM1000 was back at Southall for another handover, this time in May 1987 when the bus was being collected by the present owners to be saved for preservation.
The photos reproduced below were taken by members of the RM1000 Preservation Group to record the acquisition of RM1000, but they also show the Works eight years after closure.  AEC was no more, and what was left of the Works was being used by LT for preparing redundant buses for disposal.
C L I C K   A   T H U M B N A I L   F O R   A   L A R G E R   I M A G E
RM1000 just inside the Works,
with other Routemasters and Leyland-Nationals.
Close up of RM1000 inside the Works.
RM1000 outside the main gate. Note the triangular hole in the gate post where the AEC badge was.
This view shows the boarded-up showroom to the left of RM1000.
Another shot of RM1000 at the main gate.
Although derelict the Works frontage and drive still look impressive behind RM1000.
Many thanks to Martin Rickwood of the RM1000 Preservation Group for forwarding these photos.