In Dishforth's case, Leeming's OC Station Services Sqn (OCSSS, remember them) let me LPO (Local Purchase Order, remember them) every pack of Vapona to be had in Boroughbridge.
24 hours later every bluebottle was dead.
The snags then arose,
Snag 1. Walking across the carpet tiles was rather akin to walking on a shingle beach, very crunchy. Trusty vacuum cleaner sorted that.
Snag 2. I may have overdone the Vapona. After an hour or two's exposure to the fumes, the staff were also feeling a bit crunchy.
Snag 3. Trying to obtain a volunteer (with strong stomach) to dispose of the various dead rats/pigeons and other wildlife that had set up home in the ATC Plant Room.
Danny, you asked where do flies go in winter. The blo*dy Plant Room at Dishforth ATC, that's where.