If you want to see a picture of the cap go to the following site
http://www.iaopa.eu/mediaServlet/sto...10/pp36-39.pdf
The famous gap became apparent to the BA crews in the very early days of operation to Bahrain. In those days there was limited storage for all the manuals on the flight deck and they tended to end up on the floor.
On one trip outbound to Bahrain at M2.0, a very very senior F/E decided the "Cruise Manual" fitted quite nicely into the gap [ between the rear of the F/E panel and the circuit breaker panel], and there it stayed for the rest of the flight. Unfortunately this manual also contained the tables for P7 and Fuel Flow settings, which would be required for take off.
So prior to the next Take off the manual was reached for[ so as to get these setting] only to find the manual was jammed tight in the gap and could not be removed. Fortunately another manual on board also had these graphs and so the settings could be found and set for the take off, which saved a very red face.
The famous gap became a common talking point when visitors came to the flight deck, with them being invited to put their hand in the gap at Mach 2.0 and then just before they got off to come and see if they could put their hand in the gap then.