THE Met Police has cut its "speed tolerance" by 1mph, leading to a 259 per cent increase in drivers being penalised for speeding.
New, tougher rules aiming to stamp out the offence mean that 347,000 drivers have been warned they will be prosecuted for driving to fast in the past six months.
This compares with just 97,000 in the six months running up to the change.
"Speed tolerance" guidelines set out the leeway motorists get for going over the limit.
Under the previous rules, cops set the prosecution threshold for speeders at 10 per cent of the speed limit plus 3mph.
This meant that those driving under 25mph in a 20 zone would not face action.
However, new guidance has reduced this to 10 per cent plus 2mph, cutting the boundary to 24mph in a 20 zone.
The new rules were introduced in May 2019, but not announced, and have led to a significant increase in speeding prosecution.
A statement from The Met said: "Posted speed limits are the maximum speed that road users should travel at any time... irrespective of the speed threshold that police commence enforcement action."
Other police forces still use the 'plus 3mph' formula but the National Police Chiefs Council says it intends to review national rules.
AA president Edmund King said tougher enforcement could lead to drivers using 'smart limiters' which restrict fuel supply and sound an alarm to get drivers to reduce their speed.
Mr King said: "If drivers struggle with the limits, most modern cars have speed limiters and often sat navs will flag up speed warnings.
"It is not worth chancing your licence or indeed a potential road collision by relying on unwritten levels of tolerance."
Meanwhile, Steve McNamara, general secretary of the Licensed Taxi Driver's Association, told The Times that there had been "an absolutely massive increase in taxi drivers receiving three, six, nine and 12 points in a three or four-week period"
He added that some of these drivers "have been driving 35 years as a professional driver without a single point on their licence."
Mr McNamara used the example of Park Lane, London where he claimed drivers were "getting aught at three o’clock in the morning for doing 23 miles an hour and losing their livelihood."
Park Lane used to have a 40mph limit.
Scotland Yard says that if a pedestrian is hit by a vehicle at 20mph, they are five times less likely to die from the crash than at 30mph.
