This is the best link to report a problem
https://www.fillthathole.org.uk/hazards/report
Edit - Sorry, just realised it’s in the link above
That's good for people who don't know where to turn, but if you do, the best way of reporting is really to the appropriate authority directly.
Why? fillthathole does the work for you, means your reports are in one place, means you're not scattering so much info around. What advantage is there to reporting directly?
@Oliver Schick started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
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This is the best link to report a problem
https://www.fillthathole.org.uk/hazards/report
Edit - Sorry, just realised it’s in the link above