Howden Helicopters were still spraying in the UK as late as 1993 with Bell 47's.
Manfriday helicopters were bracken spraying with R22's around the same time maybe later.
Bond sold their Hillers in 1986 to a company in Lincolnshire who were also spaying with a 206. Around that time Agricopters sold their Hillers to a couple of Greek companies. G & SG Neal still had a pair of Hillers spraying around this time as did Tom Clark (Helicopters for Industry).
Not sure when any of them finally finished. The back end of the 80's was the death knell of spraying in the uk.