Try parking your car anywhere near plac Zawiszy and see what happens. I've lived in London too and Warsaw wins hands down.
UK - The total number of prostitutes is not known and is difficult to assess, but authorities and NGOs estimate that
approximately 100,000 persons in the country are engaged in prostitution
Poland - The total number of prostitutes in Poland is not known, estimates vary widely and should be interpreted with caution. For instance, the US 2009 Human Rights Report states that: "according to police there were an estimated 3,300 prostitutes in the country; however, NGOs estimated that there were
18,000 to 20,000 women involved in all aspects of the sex industry
Hands down?