If you aren't British, contact the consulate from your country. If your country does not maintain a consulate or embassy, they should have an arrangement with some other country to at least relay information and give you minimal help.

Also, notifying your consulate of even simple things, like a robbery, helps them understand the crime situation in the country. If you don't believe the police will help, or the police actually perpetrated the crime, your consulate is definitely the place to report the incident.