There are free WiFi zones in some local libraries where you can do just that. For some excuse (sorry reason) along the health & safety lines (I think - mind goes blank, ears close), you can't be connected to mains power supply so your battery needs to be fully charged up.
However all other hotspots require you to join a provider and pay.
At the moment, WiFi is free from Cloud in the City of London but that is only for 1 month.
Hope that helps.