Green’s Dictionary of Slang

1. (UK gay/Und.) any street that is known as a centre for prostitution, e.g. Piccadilly, Oxford Street; King's Cross in Sydney.

1959		C. MacInnes Absolute Beginners 71: We’d now reached a street down near ‘the Front’, as the girls on the game call the thoroughfare.
1977		D. Powis Signs of Crime 184: Front, the Oxford Street.
1985		R.G. Barrett You Wouldn’t Be Dead for Quids (1989) 108: There’s a bunch of coppers [...] going up and down the front all the time Sunday night.

2. (UK teen) the main street of a gang’s territory.

1989

J. Morton Lowspeak 61: Front [...] the main street.