Sex in the City could have been written about Liz Carr and Penny Pepper. Carr, 34, fresh from the Edinburgh festival, is still excited about the rave reviews for her Fringe show Bravetarts, one of which described her as "unapologetically dirty". She considers herself to be a modern, liberated woman and describes herself as semi-single - she has been seeing a married man for the last few years, retaining the freedom to date anyone else.

Pepper, slightly older than her friend at 42, is a writer and performer who describes herself as "very sexually orientated", readier than ever to discuss her own needs and desires having just split up with her second husband.

We would be in Samantha Jones territory here, but for one critical difference. Both women have disabilities and use wheelchairs. Many readers may feel that this subject matter is outside their comfort zone - it is a reaction that both women face on a daily basis.

Sex education is widely believed to be a key part of secondary education, and a vital part of establishing a healthy sexual identity. But while sex education generally is an area about which many people feel insecure and uncertain, those with disabilities are in an even more difficult situation. Not only are they often not given sex education appropriate to their needs, in many cases - especially outside mainstream education - they may not be taught about it at all because parents and teachers often shy away from explaining the facts effectively. When Pepper was growing up in the 70s, the idea of sex education for disabled people was simply not an issue, because no one believe they needed it.

It has been a long journey for Pepper, especially because she spent much of her childhood in and out of hospital for prolonged periods. There was never a hint that someone like her could expect to enjoy any sort of sex life. "When I was 16 a close friend told me about masturbation and that changed my life," she says.

"I couldn't wait to try it and it was simply wonderful. But I couldn't believe that no one had talked to me about my sexuality. It's so much part of who you are but when you are disabled it's almost as if you should be totally asexual."

That tentative beginning eventually lead to sexual exploration with various partners, but Pepper was well into her 20s before she felt confident enough to recognise that other people might find her attractive. "I was very nervous and didn't have the usual teenage experience of growing up and being aware of myself as a sexual person," she says.

"All the emphasis on 'the perfect body' doesn't help, especially since there's no way I could ever aspire to what is seen as ideal. Being in a wheelchair limits my ability to move in what you would consider the standard sexual ways. It can be hard enough discussing sex with an established partner, never mind having to be upfront from the start and really spell out the realities - for example, telling someone it hurts when he does that, I have no feeling there or I physically cannot manage to do that. That takes a lot of confidence, especially when you compare it to the popular media images where couples just melt into each others' arms and the sex is instantly wonderful."

People tend to make assumptions about people with disabilities that have no bearing on reality - or their humanity. Pepper is clearly tired of trying to change these. "Part of the problem is that we're seen as ill, which isn't attractive at all," she says.

"People are drawn towards good health - I'm sure we're genetically predisposed towards it - so unlikely to automatically consider someone who appears to be ill as a sexual being. I'm always struggling with the way society defines me."

And Pepper's fight isn't just about herself. She has tried to change perceptions creatively and usefully, and began by filling the gap in knowledge that had so held up her own teenage sexual growth, writing a helpful sex guide for people with arthritis, complete with illustrations of practical sexual positions.

Her second book, Desires, is a collection of explicit fiction about disabled people, relationships and sex, and now she has a play, Bye Baby Bunting, going into production at Jacksons' Lane theatre in Highgate, north London. "Set against a background of domestic violence, the central character is disabled and going through rites of passage. She is becoming aware of her sexuality," says Pepper.

"The play probably sums up what I want to do through my work and in my life - to challenge the status quo about disability, gender and sexuality and explore definitions of self and identity."

Liz Carr would like to aim for all that and more, but through a different medium - the unforgiving spotlight of stand-up comedy, which she has been doing on the national club circuit now for a year. "I love being on stage and engaging an audience on any subject, but redefining their view of disability and sex is always a good one. The shock value is really high, especially when I talk about the practicalities of growing up disabled - how likely is a sex life when your mum has to take you to your date?"

In her case, a mainstream education highlighted the differences between Carr and her friends, which made it hard for the teenager to imagine herself with a sexual identity. "They would tell me what they were getting up to with boys and it was a million miles away from anything I thought I would experience," she says. "My sex life didn't start until my mid-20s when another wheelchair-user changed everything for me by telling me that anything was possible. Why had nobody done that when I was growing up?"

Even people who have no problem understanding that people with disabilities do have sex lives commonly assume that their partners will be similarly disabled. But all Pepper's partners have been able-bodied and Carr admits that when she first started experimenting sexually she did not want to go out with someone with a disability, preferring to distance herself from the "disability thing" as much as possible. Now she is much more open to the idea of simply dating anyone she finds attractive and agrees that it has a lot to do with being comfortable with her own sexuality and assuming the same of others.

Although neither woman claims to be a spokesperson for other people with disabilities, they both admit to worrying that the situation has changed little over the years. "People make assumptions about disabled people in a way they never do about others and that is hard, says Carr. "Like so many women of my age, I'm happy and fulfilled with a great sex life - does that shock you because I'm disabled?"

· Penny Pepper and Liz Carr are interviewed on Blusher's Guide To Sex on Radio Scotland (www.bbc.co.uk/radioscotland) or on digital satellite 0116; Freeview 89 or Cable 869/931 on Thursday August 24. Desires by Penny Pepper is published by Bejamo Press, priced £6.99.