Hendon – the Metropolitan Police's training school.
Nick - either
a) to make an arrest. ‘We wait outside the window and nick them when they come out with the TV…’ or the ever popular; ‘You’re nicked my son.’
b) a Police Station, presumably because it’s where you take people once you’ve nicked them. Hence ‘My nick’ ‘Down the nick’ or used as part of proper name ‘Charing Cross Nick.’c) to steal. ‘Oi you nicked my telly’.