Slang for a Nazi or fascist pig. Derived from the brown shirts worn by the Sturm Abteiling (SA). Brown was the color of the Nazi party in the 20's and 30's, much as red and blue are respectively associated with the Republican and Democratic parties in the US now.
Side note - the Schutzstaffel (SS) primarily wore black uniforms.
Employees of the Tax Credits Office of Her Majesty's Revenue & Customs (HMRC). Derived both from their role as enforcers for Gordon Brown, and their enthusiastic embracing of Social Justice & Human Rights values not seen since the fall of Nazi Germany.
'I don't believe it, love - the Brownshirts have just phoned demanding we pay all last years Tax Credits back or they'll take us to court'