Many motorists exceed speed limits because they have been "tailgated" by more aggressive, law-breaking drivers close to their rear bumper, according to new research.
Instead of slowing, bullied drivers react to the intimidation by putting their foot down, even if it means breaking the law themselves.
Road safety experts said the research underlined the importance of drivers resisting the temptation to tailgate other motorists. The practice is estimated to be the cause of 7 per cent of UK road traffic accidents.
In one of the most detailed studies into how and why Britons speed, experts from the Transport Research Laboratory (TRL) sat with drivers as they travelled the UK's roads.
They observed "guinea pig" motorists speeding up as they were "pushed" to go faster from behind. They also found drivers who stuck to the speed limit suffered four times as much tailgating as those who did not.
TRL researcher Nick Reed said most motorists they looked at broke the Highway Code. "More than 80 per cent in our study exceeded the national speed limit, left insufficient gap distances to the car in front and failed to check mirrors and blind spots," he said.
"These traffic violations and errors may be partially attributed to the attempt to avoid frustration and the aggressive driving of other motorists."
The research underlined road safety campaigners' concerns that too many drivers are allowing their decisions to be effectively taken by others. It even recorded how motorists' heart rates – and stress – rose as they were tailgated, spurring them to go faster.
Traffic police say drivers are increasingly being forced to increase their speed in response to pressure from other motorists. "We see it time and time again," one senior officer said yesterday. "Somebody sees another driver too close in his rear mirror and he panics, gets intimidated and makes a forced error, a stupid error they would not otherwise have made.
"He ends up coming to grief and, more often than not, the guy tailgating them does too."
Police and prosecutors rarely have any sympathy for a speeder or tailgater who claims he or she was forced into driving badly.
Justice system insiders stress the only real excuse that will stand up in court is that a motorist was speeding to get out of the way of an emergency services' vehicle.
A "ton-up" speeder in England escaped a ban in 2006 after claiming to have been "intimated" by a police car behind him.
Constable Scott Marshall, a road safety expert at Strathclyde Police, said motorists shouldn't expect sympathy if they speed because of others, or if they stray too close to drivers they think are going too slowly for the road conditions.
He said: "Don't allow others to intimidate you or force you to make an error. If need be, slow down and let them pass. You cannot blame your error or bad driving on someone else."
Neil Greig, policy director of the Institute of Advanced Motorists, agreed. "A mature driver does not allow themselves to be bulled by other drivers," he said. "You can't just blame the other driver: you control your own destiny.
"In reality, people do need some strategies to avoid being bullied. If you are being pushed along by another motorist at a speed you don't want to go at, then you can just let them past.
"I've seen it on the M8, when there are queues of drivers speeding in the fast lane. Pull over: don't get involved."
Greig, however, stressed that drivers who insist on forcing other motorists to obey the rules of the road could also get themselves into trouble. He warned of the dangers of "self-righteous" drivers – those who, when tailgated, try to stop their tormentors speeding.
"Reacting to somebody else's bad driving is a recipe for disaster. If you slow down or brake when you are being tailgated, you have become the bully in the front. If you want to take the moral high ground, make it clear you are going to move out of the way, and do so," he said.
TRL researcher Reed, meanwhile, discovered many drivers were unaware of their own bad habits. Motorists in the study often tailgated others, even after complaining about the behaviour. He said: "Ninety-three per cent of our test drivers were tailgated while driving to strict Highway Code guidelines. Just 47 per cent of those who drove as they normally did suffered the same way.
"However, it is possible that it is so commonplace that it has become ingrained in driver behaviour, as many of our test drivers also tailgated once they were free to drive 'normally'."
A spokesman for Direct Line insurance, which sponsored the research, said: "Impatient drivers may also be surprised to hear that, by driving less erratically, with fewer gear changes, rapid accelerations and decelerations, the average journey time is 8 per cent faster."
Scotland's fastest speeder was banned from driving last year. Hairdresser Neil Purves was clocked at 166mph on his Suzuki GSX-R1000 motorbike in the Borders.
Men account for 81 per cent of speed convictions in the UK.
Nine out of ten British drivers polled by road safety charity Brake admitted they exceeded the speed limit; but two-thirds said they wanted tougher penalties for speeders who kill.
Scottish Government research has found that drivers who are caught speeding are nearly twice as likely as the average to have been involved in a recent accident.
Scottish speed cameras raised 4 million in fines in 2008-2009, less than the 7.2m cost of maintaining them.
UK Government research found speed alone caused more than a quarter of fatal road accidents.