Why the war between drivers and cyclists?

A motorist's tweet boasting about hitting a cyclist created uproar when it went viral. What does it reveal about the battle on the UK's roads?

Toby Hockley was on the 100-mile Boudicca Sportive ride in Norfolk when he says he was struck by a car and flung into a hedge. The driver didn't stop. Hockley emerged from the hedge, sore but intact.

It sounds like a run-of-the-mill depressing incident from the UK's roads. But the shocking part came later.

A young woman tweeted: "Definitely knocked a cyclist off his bike earlier. I have right of way - he doesn't even pay road tax! #Bloodycyclists."

The post was retweeted hundreds of times and took on a life of its own.

Soon cyclists had informed the police, identified the woman, tracked down where she worked and told her employer.

Norwich Police tweeted the woman back and told her to report the collision at a police station. "We have had tweets ref an RTC with a bike. We suggest you report it at a police station ASAP if not done already & then dm us".

Police have contacted both the cyclist and the tweeter and are investigating.

The incident and the speed of the backlash on Twitter with the hashtag #bloodycyclists being appropriated by bike users, highlights the simmering tension on the UK's roads.

"I am a #bloodycyclists just trying to get about London. Would be nice not to risk my life every morning just trying to get to work," tweeted @lennyshallcross.

There appears to be a burgeoning, visceral anger in the cyclist-driver relationship.

The recent explosion of cyclist numbers in the UK's cities has changed the dynamic of driving. In heavy traffic cyclists are often the fastest things on the roads, more agile at getting through gaps than motorbikes.

Drivers do not always see them. They may forget to check their mirrors. It can be difficult for bikes getting through clogged traffic with lorries and vans blocking both sides of the lane.

Cyclists complain of drivers winding down their windows to hurl abuse. Drivers make a similar complaint about being shouted at.

Cycling campaigners are calling for a new law in Scotland to make motorists automatically at fault in an accident. The UK is one of only five European countries - Cyprus, Malta, Romania and Ireland being the others - that does not currently have the "strict liability" law. Some cyclists now wear helmet cameras to record anti-social behaviour.

The cyclists' response to the Norfolk tweet is a sign of the growing social media "enforcement" action taken against drivers who are seen as having either endangered or threatened two-wheelers.

"It's relatively common because there are a lot of cyclists out there with helmet cams and they will post licence plates and video of bad motorists," says cycling journalist Carlton Reid.

Then there are deliberate attempts to scare cyclists, some commentators allege. "Many cyclists have been on the receiving end of 'punishment passes' [driving to instil fear] which can be extremely close, or can even see people being hurt," says Reid.

In 2011, 107 cyclists died on the roads in Britain and more than 3,000 were seriously injured, according to the Royal Society for the Prevention of Accidents.

But there's a flipside. Cyclists, to many drivers, are serial flouters of the rules - jumping traffic lights, weaving in and out of the traffic, not signalling and failing to stop at zebra crossings.

There's "huge antipathy" between people on bikes and in cars, says motoring journalist Quentin Willson.

"We've got a minority of cyclists and car drivers who are aggressive," he says. "It results in a war of attrition between two and four wheels."

Today it is perhaps less politically correct to attack cyclists than drivers - but anecdotally many will privately curse cyclists passing them in traffic congestion.

The #bloodycyclists hashtag was largely hijacked by the two-wheeled community

John Griffin, boss of minicab firm Addison Lee, has argued that an influx of novice cyclists could lead to more accidents. "It is time for us to say to cyclists, 'You want to join our gang, get trained and pay up'," he wrote.

Willson is sympathetic to the plight of cyclists. But an aggressive minority have become a metaphor for everything drivers hate. "They're dressed exclusively in Lycra and wraparound shades, they ride on the pavement, go the wrong way down one-way streets and straight through red lights. And that's why motorists hate them."

Cyclists argue that the minority who break the rules are simply more conspicuous when they misbehave. Drivers stuck in a queue of traffic have plenty of time to watch as an errant cyclist jumps a red light, for example.

There is also a sense of frustration as car drivers watch a pedal-powered vehicle overtake them. "The very fact that cyclists are able to filter through traffic grates on many motorists and they take that out on cyclists," says Reid.

The tweeting motorist's claim that she had a greater right to be on the road because she paid road tax is a widely held but inaccurate belief, says Reid, who runs a blog called - with deliberate irony - ipayroadtax.com.

The reality is that there is no "road tax", he says. Road construction and maintenance is paid for by everyone through general and local taxes. The Vehicle Excise Duty that motorists pay is levied according to engine size or CO2 emissions.

Is it time for the return of the cycling proficiency test?

Critics miss the point that bikes don't emit CO2 and that many cyclists also own cars and are paying VED anyway, he says.

While there is bad behaviour on both sides, it is an unequal relationship. The driver is protected by a metal shell while the cyclist is exposed.

"It's scary as a cyclist because you are the vulnerable road user," says Rob Spedding, editor of Cycling Plus.

"You have someone in a few tonnes of metal bearing down on you and you are just flesh and bone. It's potentially fatal."

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