The Pathfinder Year - 97 Squadron at Bourn
Lancasters moving towards the runway, prior to take-off
This is a still from "Night Bombers", a film made in 1943 about No. 1 Group Bomber Command at RAF Hemswell in Lincolnshire.  (Identified by David Layne.)

Though it is not of Bourn, it is entirely representative of what these extremely dramatic massings of Lancasters prior to an operation were like. You could almost be standing at the top of the runway at Bourn, watching them coming up by the Control Tower.