Green’s Dictionary of Slang

(UK Und.) a false accusation or perjured evidence used to have an innocent suspect (albeit one who has a criminal record) arrested and found guilty.

1970		G.F. Newman Sir, You Bastard 71: [Barristers] rarely brooked any suggestion of police brutality or fit-ups.
1989		in G. Tremlett Little Legs 121: Chopper takes £500 round for her and it was a fit-up.
1998		I. Welsh Filth 59: This is a fuckin disciplinary fit-up.