why are policeman called pigs?

[quiltfanatic]

Where did it come from calling a polceman a pig?

[Quizmonster]

The word 'pig' has been used as a term of contempt for someone very much disliked for about half a millennium. There is even a reference to a Bow Street Runner - an early policeman in London - as a 'pig' from about 200 years ago. Only in the 1960s, however, when street protests became common did the word gain wider usage.

[Steve_ref]

BritSlang by Ray Puxley quotes:

" A police officer, a piece that's been around since the early 19th century but found universal fame during middle of the 20th. 'Swine gums' - said to be a copper's favourite sweet."