Osmand, that favourite of cycletourists (not sure if that includes boris) actually allows you to search for brothels and does find some. A great app, but its rather unintuitive front end (ooer) can mean serious grappling through its innards. Which is how i strayed across this.
Edit, just checked, it's a poi category under "leisure".
Edit edit, i should stress that when i say it finds some, i have not personally rolled up on one of my tourers, unhooked my panniers and bibs and checked out these venues' credentials. Maybe someone knows pandora"s in wilmslow.