Green’s Dictionary of Slang

garrotty adj.

also garrity
[? SE garrotte]

crazy, insane.

[UK]J. Sullivan ‘Hole in One’ Only Fools and Horses [TV script] I don’t believe it! I do not believe what that garrity old git has done to us!
[UK]J.J. Connolly Layer Cake 288: Old bill would scream about it, they’d go garrotty.