Green’s Dictionary of Slang

the anus; one of a number of sl. terms relating to the colour of excrement.

1997		Roger’s Profanisaurus in Viz 87 Dec. n.p.: Bourneville Boulevard euph. Arse; fudge tunnel. Used to denote homosexuality, as in: ‘I believe he strolls down the Bourneville Boulevard’.
2013		N. Williams Unfaithfully Yours 230: It is not just a matter of fishing out the old penis and shoving it up the old slippery. You can squeeze their behinds all you like. You can get down and dirty on the Bourneville Boulevard if that is what takes your fancy.