Sheep scab is a cruel disease spread by the sheep scab mite probably affecting flocks since Biblical times.
In the UK it was made a notifiable disease in 1869 (though legislation to control it goes back to King Hywel the Good in 949, more info here).
By compulsory treatment or destruction of infected animals coupled with health checks on imports it was eradicated in GB by 1952. Wherever the disease had been found whole flocks were dipped under police supervision as in this film clip from 1939. Eradication continued through the war years, this clip from 1943 [contains gender stereotyping but note absence of protective clothing].
In 1972 a lapse in border controls at Birkenhead re-imported the disease and in 1976 MAFF re-introduced compulsory dipping. This time police were largely replaced by MAFF inspectors but the main difference was the products used successfully in the 1930's (which required redipping within 14 days to control mite eggs) had been replaced by stronger single dip organochlorides and organophosphates.
For environmental reasons organochlorides were banned in 1984 (as subsequently were synthetic pyrethroids) leaving OPs as the only licensed products.
A brief history of the damage caused is listed here.