I can even date the picture for you:
1. No dog section on the airfield so pre 2003.
2. WP840/G-BXDM was sold to Halton Aero Club by the artist Michael Turner in 1999.
3. Also no other Apprentice airframes on the airfield so definately after 1993.
4. No A41 dual carriageway so pre-2002
So I deduce the picture was taken in 1999, 2000 or 2001 - how did I do?
The B Word
PS - it is definately the Finlay Gym. Named after Gp Capt Don Finlay - Battle of Britain Pilot, silver/bronze winning Olympian and a Halton Apprentice (or 'brat').