It started out as a joke about how the only off-roading that Chelsea tractor drivers ever do is when they mount the kerb outside the school gates to pick up little Jasper or Sophie. Now the campaign against 4x4 owners has turned ugly. Car makers say fringe activists who feel they have won the class war against foxhunting are demonising motorists because they need a new target.

Jane Riley, a freelance designer who lives in west London, has suffered taunts, swearing and vandalism since she began buying 4x4s. She has been so shaken by her recent experiences that she refuses to be identified in photographs for fear of more attacks.

Her Porsche Cayenne had its badge ripped off and people have twice dragged sharp metal objects along the paintwork. Her previous car, a Nissan 4x4, which she bought to tow a horsebox, had the words “eco w*****” scratched on the roof and sides. Riley reported the damage — about £6,000 worth — to the police but was told the chance of catching the perpetrators was small.

“We’ve had people shouting at us, not letting us out at turnings, and the worst experience was when another driver spat at my six-year-old daughter and me. We were just moving along in slow traffic and this man was staring at us, then suddenly he spat. Now my daughter often asks if we can walk instead,” says Riley.

“The hostility has grown with all the publicity about 4x4s but the police don’t seem to care. I’m not the only one. I’ve seen lots of other 4x4s which have obviously been vandalised.

“There is a woman at my daughter’s school who has a Volvo 4x4. She has four children and goes to the country a lot but she’s selling it because she’s sick of all the people swearing at her and cutting her up. She’s sick of constantly having to justify herself.”

Riley’s anecdotal evidence is backed by the latest statistics. Direct Line, the insurance firm, says claims for vandalism of 4x4s are on the increase. “There is a lot of anti-4x4 feeling and our claims team has seen a general increase in malicious damage against this type of vehicle, particularly in London,” said Emma Holyer, a spokeswoman.

The AA says its insurance records show 4x4s are more likely to suffer vandalism, even though such vehicles are no more accident prone than other vehicles.

Environmental campaigners argue that 4x4s use more fuel and produce more carbon dioxide than other cars — a problem that they claim is changing the climate. Groups such as the Alliance Against Urban 4x4s say the vehicles are unsuitable for city motoring, taking up more space, adding to congestion and presenting a greater danger to drivers of smaller cars and pedestrians.

Those on the other side of the debate point out that many 4x4s are no more polluting than some sports cars or large saloons and are no more dangerous to pedestrians than vans, trucks and people carriers. “Ultimately, congestion is not about what people drive, but where and when,” says Philip Hale, a spokesman for the RAC. “To censure or demonise a particular type of vehicle is utterly impractical and the arguments against 4x4s just don’t stack up.”

The war has intensified as 4x4s have become more popular in Britain. Annual ales increased by 12.8% to 179,439 in 2004, sparking combative exchanges between owners, manufacturers and environmentalists.

Last week Greenpeace executed a stunt it said had taken eight months to plan. Dressed in orange boiler suits, 30 protesters mingled with workers arriving for the 7am shift at Land Rover’s Solihull site in the West Midlands. They chained themselves to cars and machinery, halting work for almost eight hours and stopping the production of about 70 Range Rovers, valued at about £4m.

Greenpeace says it has no firm plans for more direct action but Steven Tindale, executive director of Greenpeace UK, claims it is “criminal” that the petrol version of the Range Rover does only 12mpg in town (the official figure is 13.4mpg).

Across the Atlantic, where more than 20m Americans drive SUVs, anti-4x4 campaigners have resorted to more extreme means of persuasion. There have been violent clashes between owners and activists. Growing resentment has led to attacks on SUV dealerships, burning of parked vehicles and even “Key an SUV” week, when some militant groups encouraged their supporters to indulge in vandalism, one website asking “Why should we do it?” before arriving at the simple conclusion: “Because it feels good.”

The Earth Liberation Front encourages its supporters to carry out arson and acid attacks on SUVs and claims to have activists stationed throughout Europe. Another web group, calling itself Stop Elmer Fudd, stops short of telling its supporters to indulge in vandalism, claiming it “does not look good in the media” and “could cause more environmental damage than it stops”, but includes pictures of burning vehicles and admits “we love to see those gas-guzzlers burn”.

UK campaign groups insist their protests are non-violent, but growing evidence points to the emergence of a more militant fringe. The Alliance Against Urban 4x4s claims to have active groups in towns and cities across the country. The group is planning its largest nationwide demonstration on July 16. Protesters stationed alongside urban roads throughout the UK will offer to throw mud on 4x4s, in a reversal of the “squeegee merchants” who offer to clean your windscreen while you wait at the traffic lights.

“We will be offering to put mud on 4x4s so the drivers don’t look so stupid,” says spokeswoman Sian Berry. “These cars were meant to be driven off-road, but most of them will never see anything more challenging than a speed bump.”

Berry insists nobody will have their vehicle muddied against their will. “We are completely opposed to any sort of vandalism or verbal abuse. We think the way to change people’s attitudes is by persuasion. We like to use humour, rather than aggression.”

The Alliance wants to see the introduction of a new tax band — G for gas-guzzler — that would see owners of the most polluting vehicles paying as much as £1,000 per year in road tax. It also wants higher congestion charge rates for the most polluting vehicles in London.

Land Rover rejects the criticism. “Land Rover is a leading British business which exports 70% of its production and makes a significant contribution to the country’s wealth creation,” says Don Hume, a company spokesman. “We take our commitment to the environment very seriously. We have consistently found many of the claims made by Greenpeace to be misleading and incorrect.”

Honda points out that its CR-V 4x4 has a higher mpg figure and lower carbon dioxide emissions than some smaller family saloons.

Riley is equally unbowed. “The Porsche is tainted for me now. But I don’t want to just give in. I’d rather just get a f***-off sports car with a massive engine,” she says, wickedly. “Something really juicy.”