Volunteers armed with a speed gun found 28 drivers breaking the 20 mph speed limit in Long Lane during a two-hour period - but the police failed to send out warning letters to the keepers of the vehicles involved.
The Metropolitan Police runs a Community Roadwatch scheme which trains volunteers to use hand-held speed guns.
The idea is that warning letters are sent to the registered keepers of vehicles found to be breaking the limit.
However, the SE1 website has discovered that despite 43 vehicles being found travelling above the speed limit on two SE1 roads in January, no warning letters were sent out.
Volunteers spent two hours monitoring speeds at the Grange Road / Spa Road junction on the afternoon of Wednesday 18 January.
The SE1 website made a freedom of information request to the Metropolitan Police to find out how many warning letters had been sent as a result of the operation.
The answer was that no letters had been sent, effectively defeating the purpose of the whole project.
The Met told us: "The scheme relies, as an educational activity, on impressing upon drivers the consequences if they had been detected by an officer.
"As such, letters are sent to registered keepers adhering to the 14 day timescale in place for traffic prosecutions.
"Unfortunately on these two occasions we were unable to get the notification letters out to the registered keepers within that self-imposed timescale."