I doubt any aerial crop spraying now takes place on the UK lowlands. Government figures for 2002 (the latest I can find) show no fixed wing operations with spraying mostly confined to bracken on moorland. PDG Helicopters at Dalcross Inverness do a lot of forestry spraying in Scotland.

Ludham in Norfolk was a base for crop spraying many years ago.I seem to recall Chafers operated crop sprayers from Bourne in the 60's.
Here are a few earlier pictures of a demonstration in Wales in the 1950's.

Anyone know what this helicopter is?