The TGA Supersport tends to be bought by people who were fond of motorbikes in their youth, and many of its owners know it affectionately as the Harley, because its high silver handlebars supported by chrome springs are immediately reminiscent of the brand. It's a Hell's Angels look for people with limited mobility.

This is boom time for the mobility vehicle industry. The Supersport is one of hundreds of vehicles on display at the annual show of mobility scooters at the Birmingham NEC this week – a mini automobile trade show (but with medical mannequins instead of models in bikinis). Over the past decade, the stigma around these vehicles has eroded, and they are increasingly popular with younger people. Manufacturers are responding by trying to take the product away from its staid, slightly mournful medicalised roots and promoting it as a fashionable lifestyle accessory.

Some of the new brand names are startling. There is the Vegas scooter, displayed spinning on a rotating roulette board; the brochure explains it's a lightweight model capable of carrying a driver up to a maximum weight of 21st, with a top speed of 4mph. Taiwanese motorbike manufacturer Kymco has shiny new designs that look like trim four-wheeled Vespas and come in lovely boiled-sweet colours ("golden lemon" and "flame orange"). Electric Mobility has a more heavy-duty item in sleek silver, which can travel up to 8mph, is fitted with a USB port so you can recharge your mobile and plug-in your SatNav or iPod, and is marketed as the Rascal (yours for around £4,500).

These vehicles have transformed life for millions of people with disabilities. Shaun Greenhalgh, 56, from Wigan, has had difficulty walking since he slipped and ended up with several prolapsed discs when he was in his early 30s. He has been using a scooter for 24 years and now owns four. "Like most scooter users, I can walk to some degree, but only with pain and discomfort," he says, as he examines the models on display at the exhibition. "Without it, I would have no life. They might as well have put me down."

But as they have become more popular, mobility scooters have become more controversial. Although the main growth in the market is the consequence of an ageing population, there is evidence that people with no disabilities are beginning to buy the scooters on the secondhand market (where they can cost as little as £100) because, with no tax, licence or insurance requirements, they provide a cheap alternative to cars for getting around town, particularly at a time of rising petrol prices.

Strictly speaking, it's illegal to drive one without a disability, but it's a grey area and politicians recently called on the government to bring in clearer regulations. Transport minister Norman Baker has promised to investigate. In new guidelines published last month, he recognised that the shopping scooter was in the process of being revolutionalised as a concept, declaring that he had "decided that the legal term 'invalid carriage' should be replaced with a more suitable and contemporary term" (without specifying what that term might be). Responding to reports of rising accident numbers, he also reiterated that drivers should not be drunk and need to have good eyesight.

The steady rise in sales of these vehicles is evident in their inescapable presence in shopping centres, rural town centres, and high streets all over the country. Weirdly, there are no industry statistics that give an accurate sense of how the market is growing, but the Department for Transport offers estimates, suggesting that there are around 250,000 to 300,000 on the road across the UK, four times the total five years ago of around 70,000. Mobility scooter shops have opened up in most medium-sized towns in the past decade (also offering specially designed armchairs and beds for frail and older people).

None of the suppliers will reveal their sales figures, but around 60-70,000 scooters are thought to be sold here each year. No other country in Europe is selling as many (with the possible exception of Holland, where bicycle use is very high, and the mobility scooter is seen as a bike replacement for older cyclists).

There has been a marked change in the way people use them. A decade ago these were products used only by very frail people; now manufacturers are designing new models with bench seats capable of carrying people up to 40st. "It's a cultural issue. People are larger and, dare I say it, lazier," an industry spokesman says (before deciding that he doesn't dare say it, and asking for his name not to be put to the quote). "People are using them as a mode of transport rather than public transport or a car."

While users describe how these products have transformed their lives, offering new independence and liberating them from the need to be pushed around, the scooter's increasing presence – clogging pavements and traffic lanes – has prompted rising hostility.

They remain classified as medical devices and the law states that this kind of vehicle should be driven only by someone "suffering from some physical defect or physical disability" – but there's no clear definition of what that means, and the disability can be temporary or permanent. Whereas wheelchair users tend to be unable to walk, scooter users often can, but with difficulty. The anti-mobility scooter lobby is confused by the vision of people stepping off their vehicle and walking into a shop. The sense that some people are using them for convenience is stoking the hostility, and legitimate users say the public are vocal in their criticisms. Twitter is full of people complaining that users don't seem to be "disabled enough". "Mobility scooter users are aggressive sociopaths," is a typical tweet.

Toni Orchard, 39, travelled from Swindon to visit the exhibition to research the best model to buy, because she thinks a mobility scooter will improve her quality of life. She has had trouble walking long distances for the past 10 years because of her obesity, which she says has become more severe as she has got older, despite her concerted efforts to tackle it, including a gastric band.

"If I had one I would do more days out; I could go and see places rather than being put off by the amount of walking," she says. "I can't walk long distances without pain. I can't do more than go around the block to the shops. It would be great to be able to go out without worrying about which places have seats that I can rest on."

She is considering the Pride Gogo Elite Traveller or the Vegas, which is the smallest one available that will both take her weight and can be dismantled to fit in the boot of the car, but isn't sure yet that she can face down the simmering disapproval of pedestrians. She has rented scooters in the past when she visited Disneyworld in Florida, with her husband. "In the US there is no stigma at all. But I haven't much used them here. I don't know if I'll get looks as I drive down the street. Part of me thinks everyone is going to stare at me and think that I am just a fat lump," she says.

It's a hostility that her husband, who uses a powered wheelchair because of lifelong mobility problems, tends not to encounter; crudely, wheelchairs elicit understanding from passersby while mobility scooters trigger irritation.

Greenhalgh says: "If someone sees you in a wheelchair, they assume you are 100% disabled, but with us they are confused." The technology has improved vastly since he first used them 20 years ago. "To begin with they wouldn't take my weight and I'd burn out the motor. Now they come in all shapes and sizes, for all terrains," he says.

As a former driving instructor (the country's youngest driving instructor when he qualified at 21) he is very critical of people who drive their scooters irresponsibly. "The problem now is that people drive them very badly, they put them on full speed in shopping centres," he says, showing how a switch, not much bigger than a toothpaste tube lid, can be turned to the right to reach 8mph (which is the out-of-town limit; 4mph is the top speed allowed in urban areas). "It's horrendous."

The growing market in secondhand scooters, he says, is led by relatives of newly deceased users, who want to offload them quickly. He is annoyed by this increase in able-bodied users, saying they buy them "because of the fuel prices, or because they're so lazy they can't be bothered using a bike or a bus, or because they're drinkers. Go to a pub, you'll see them parked outside. We need to stop able-bodied people from using them. If every Tom, Dick or Harry gets one it will be chaos."

His girlfriend, Sue Brett-Michaels, 55, a former healthcare assistant, now redeployed in a NHS library because her severe arthritis makes it hard to stand up for long periods, says people respond negatively to seeing her on a scooter, particularly when she gets up from it to walk to the car. "People wonder why I need one when I can walk, but I can only take three or four steps. Any more is just too painful. People tut and say: 'These bloody things get in the way.' I wish I didn't need one. I would absolutely love not to be forced to use one of these."

Greenhalgh says: "I tell people: 'You can have this and I'll have your legs.'"

Alison Seabeck, Labour MP for Plymouth Moor View, wants the government to regulate the industry more closely. She is concerned that no department keeps figures for the number of people who have been killed or injured in mobility scooter related incidents. She too is worried by the growth in the secondhand market. She was shocked recently to see a woman "leap out of her mobility vehicle, rush into the shops, come back with heavy bags and spring back into it". "Of course, you can't judge the nature of someone's disability by looking at them; people with arthritis and MS have days when they feel fit, and days when they can't move more than a couple of steps, but we need to make sure that they're being used appropriately. At the moment we just don't know who is buying them. It's a real can of worms. The government has to take control."

Among manufacturers, there is a recognition that the industry will have to deal with the rising controversy. Because there are some government grants for the vehicles, this hatred of the scooter is getting muddled up with a broader, rising resentment of so-called benefit scroungers, stoked by the government's tougher rhetoric on what it describes as "idlers and layabouts", as it pushes through huge cuts to disability benefits.

Steve Perry, Electric Mobility marketing manager, says: "People have a view that there are a lot of people claiming benefits that they are not entitled to. There is some confusion. Subliminally it makes them more cynical, more hostile towards scooter users.

"But a lot of the hostility to scooters is simply because there are now lots of them. People see them in shopping centres, racing through, too fast. They are very quiet; there is no whirring noise like a car engine to let you know they are coming. But the independence they give … we get letters from people telling us that it has revolutionised their life."

Although the market is growing, there has been such a rapid expansion of companies making the product that there is less money for individual suppliers, prices have dropped and companies now are having to compete on image. Only a few years ago, buyers just got to select between burgundy or dark blue. Now manufacturers in China and the Far East have moved from golf buggies or mopeds into the market, and are offering huge choice.

Explaining the Vegas product brand, Steve Hughes, commercial director of Roma Medical, says: "We want people to feel that they are going to have some fun with it."

Tim Ross, TGA Supersport's sales manager, says his products are for ex-bikers or for "someone who doesn't want to be told: 'Right, you're old, you're disabled, so get a red scooter. It's a little bit modern, it's a bit funky."

Mark Hermolle, managing director of Kymco Healthcare, explains that baby-boomer scooter users are demanding beautifully designed and powerful products.

"An earlier generation would say: if I can't get there with my stick, I won't go anywhere. But scooters have become much more acceptable. Scooters are an extension of yourself. Just as you think, 'I can either buy an ugly suit or a smart one', the same is true of scooters. People take pride in these products. They don't want to look as if they are driving around on an old bread bin."