In London, if you see a streetlight out or other fault on TfL's network, you can report it through the FixMyStreet.com website from the excellent MySociety (also known for WhatDoTheyKnow.com).

E.g. https://www.fixmystreet.com/report/9023901

Unfortunately, not all boroughs (including, sadly, Tower Hamlets) take reports through FixMyStreet.com, but the site will let you know who is responsible for an area and give you links to their reporting contacts or forms.