Lady Grey-Thompson may be Britain's greatest Paralympian, a TV personality and a dame of the British empire, but if like her you use a wheelchair, fame and stellar achievement can count for little when confronted with the vagaries of the public transport system.

At one point this year she found herself marooned alone at midnight on a commuter train. She'd reached her destination but the carefully booked staff assistance was nowhere in sight.

"I ended up having to get out of my [wheel]chair, sit on the floor, which is not a terribly pleasant place to sit, throw my chair off the train and then crawl off," she recalled.

It was not the first time Grey-Thompson had been forced to perform an undignified all-fours shimmy on to a station platform in the early hours. She pointed out it was precisely the kind of avoidable "second-class passenger" experience that disabled people endure frequently.

"As a disabled person travelling you always have an element of fear, feeling very uncomfortable, of panic, of just wondering if you are going to get off."

Tanni Grey-Thompson was Britain's first disabled sports superstar, but she has become, almost surreptitiously, one of Britain's most high-profile disability rights activists. She straddles elite sport, politics and the media and forms a crucial, unique link between the buzzy, feel-good optimism surrounding the Paralympics, and the harsh, uncomfortable reality of life for many disabled people in welfare cuts-era Britain.

A fresh batch of British sporting stars will sweep to greater prominence as a result of the Paralympics: Lee Pearson, David Weir, Ellie Simmonds and Jonnie Peacock and others are set to stamp their mark on the wider public consciousness in the next few weeks. They will follow the path blazed by Grey-Thompson, a pioneer in perhaps less auspicious times.

"Tanni was the first UK athlete in Paralympic sports to cut though to mainstream sports followers. She was a very successful athlete, but she also had a strong sense of identity and character, and a compelling personal story," says Tim Hollingsworth, chief executive of the British Paralympic Association.

Grey-Thompson bagged a prodigious haul of wheelchair racing medals in a glittering career over three decades (11 golds at five Paralympics, five world championship golds, six times London marathon winner, 30 world records smashed). She was not the only hyper-successful UK Paralympian of her day, but her charisma, coupled with her success in the London marathon (at a time when the event became a globally televised, mainstream sporting event) pushed her to the forefront.

Her fame was cemented when, in 2000, she came third in the BBC viewers poll for Sports Personality of the Year, just behind Steve Redgrave and Denise Lewis, and ahead of David Beckham (the BBC neglected to build a ramp in the studio, so she could not come on to the stage to collect her award). At that point, with 12 years' competitive racing under her belt and seven to go, she was arguably the first disabled British athlete to become a household name.

Grey-Thompson was born with spina bifida in 1969. She walked for the first few years of her life but by the age of seven had lost the use of her legs. Her parents refused to see her disability as an impairment, and even though her father, Peter, was an architect, they refused to make adaptations to the family home in Cardiff, believing their daughter should learn to live in the real world ("We are all bloody-minded in this family," she once said).

Grey-Thompson says she was "brought up to believe that I could achieve anything I wanted to as long as I studied hard and worked at things". In her early teens, her local authority suggested she should be sent to a special school. She and her parents dug in. "Mum and Dad talked it through with me, as they did everything, and said I would go to a mainstream school even if it meant going to Wiltshire."

She went to St Cyres comprehensive school near Cardiff, where she passed 10 O-levels, four A-levels, and got a place to study politics at Loughborough University. "I didn't need special education," Grey-Thompson recalled, "I needed an accessible school. I didn't need to be learning how to make a cup of tea at 14. I needed to be studying for O-levels."

She had learned quickly to fight back against condescension and prejudice. In her teens, she was refused admission to a cinema on the grounds that she was "a fire risk". Why, she shot back, did they think she was going to spontaneously combust?

Misguided attempts by well-wishers to literally or metaphorically pat her on the back and praise her "pluckiness" are given short shrift. Being in a wheelchair, she maintains, has never stopped her from doing anything she wanted to do. The enemy of disabled sporting achievement is pity, she has suggested. "I don't want to be patted on the head and told I've done well if I haven't."

Her newspaper profiles over the years are peppered with self-deprecating references to her sporting ruthlessness: her constant mentions of her selfishness and egotism; her win-at-all-costs, only-gold-medals-matter mentality; or the time she flung her helmet at her boyfriend in frustration after losing a race. She is single-minded, but she ramps it up, as if to sabotage journalistic attempts to frame her life in mawkish, triumph-over-adversity terms.

Her straight-talking can ruffle feathers, and not just among the sports administrators of whom she has, in the past, been scathing. In 2005, she left MPs gobsmacked when she told them that Britain's prospects for success in the 2012 Paralympics might depend on how many road accidents there would be. "The fact is, we don't know some of those who will be competing in 2012 because they haven't broken their backs yet," she explained.

Others testify to the kindness and encouragement she offers to younger competitors and aspiring athletes. The Paralympic sprinter Ben Rushgrove was starting out on his career as Grey-Thompson's was winding down. He says she was a "massive help" to young athletes on "what could be achieved and how to go about training for it".

Tense and nervous after a day's competition, he recalls being seated at a dinner table with Grey-Thompson, who put him at ease with a stream of funny stories and anecdotes. "She was good at breaking the ice and the tension after a hard day. It took my mind off what was going on, and at that age I wasn't very good at that."

Grey-Thompson says she's mellowed in recent years. She had a daughter, Carys, in 2002, and was back in training two and a half weeks after the birth, a caeserean section. She completed the London marathon six weeks after that. But motherhood, she admitted the following year, had made her "gentler, more emotional and more patient … I [realised] you can't do everything at 100mph."

Like other former top athletes, she has smoothly embraced the lucrative world of the media, corporate sponsorship and motivational speaking. Articulate, and funny, she was one of the faces of the BBC's 2012 Olympics TV coverage, and will be an expert summariser on BBC 5 Live radio for the Paralympics, alongside John Inverdale.

Few who knew her during her athletics career would be surprised that she had a game plan for her post-track life, or that she has made such a success of it.

Some may be astonished, however, that within weeks of the Paralympics closing ceremony she will be back in the House of Lords, where as a crossbencher she takes an active, serious interest in disability rights, women's issues, and welfare reform.

As an athlete, she eschewed campaigning. This year she won plaudits from fellow peers and disability activists alike over a series of trenchant interventions on the controversial welfare reform bill.

In the spring, she warned that the development of the next generation of disabled sportsmen and women could be undermined by government plans to restrict disability living allowance, the cost-of-living benefit that allowed her and countless other disabled athletes to pay for the transport and equipment that opened up competitive sport to them. She is currently leading an inquiry into the impact on disabled people of ministers' plans to introduce universal credit – a move she has warned is likely to make the future "considerably bleaker" for many disabled people.

Although she champions the Paralympics and the power of sport to effect social change, Grey-Thompson doggedly punctures attempts to suggest the event will transform deep-seated discriminatory social attitudes towards disabled people overnight.

Grey-Thompson says she is happier than ever in her new role – "If it's possible, I love being in the Lords more than I loved being an athlete," she said recently.

Hollingsworth, for one, is not surprised: "Tanni has that restless energy that characterises a lot of world-class athletes, and she has that knowledge and understanding of the wider world. That's a powerful force."

Pocket profile

Born: 26 July, 1969

Age: 43

Career: GB athlete at 100m-800m distances 1987-2007, winning 11 Paralympic gold medals; board member of UK Athletics since 2007; created a life peer in 2010.

High point: Winning four gold medals in the 100m, 200m, 400m and 800m wheelchair racing at the 1992 Barcelona Paralympics after a year out following spinal surgery. She repeated the feat in Sydney in 2000.

Low point: Her tearful announcement of her retirement from competitive racing in February 2007.

What she says: "Some people may find [it] hard to understand, but the trouble is, there is this perception that walking is good and not walking is bad. For me that's not true, because being in a wheelchair has given me more mobility, not less. It's never stopped me from doing anything I wanted to do."

What they say: "Tanni has this ability to flow on a public platform ... And they are lucky if they can get a word in if anybody tries to argue with her." Her father, Peter Grey