If the court rules in favour of P, the transsexual, all transsexuals in employment will be protected under the EC's Equal Treatment Directive.
Sonia Carmichael, 34, a male-to-female transsexual, could not find employment as a woman, but was hired as a male kitchen porter. "The first week was fine, but then the women started asking me questions," Sonia says. "They called me names like 'dirty transvestite' and when I explained my situation, they said they wanted to see my breasts."
After three weeks, Ms Carmichael was sacked. She claimed unfair dismissal against her former employer, the Victoria and Albert Hotel in Manchester. But earlier this month an industrial tribunal ruled that she was not discriminated against on the grounds of her change of sex.
For Ms Carmichael the ordeal has been traumatic. She is in the transition phase of her gender change, which can produce an ambiguous appearance. She must satisfy the test of working in her chosen gender for a year prior to surgery.
Ms Carmichael has now found a new job as a kitchen porter and has explained her position to the management. "I've been there four months, the atmosphere is totally different and the issue just doesn't come up in discussion," she says.
For transsexuals, some professions are totally denied them, such as the Armed Forces, and in others, like the police, opportunities are limited.
Even applying for jobs is difficult. As UK law does not permit transsexuals to change their birth certificates, a transsexual can either choose not to inform a prospective employer and consequently face dismissal at any point, or can risk rejection.
Mark Rees, 54, chose to tell prospective employers about his transsexuality, but his honesty led him to the dole queue. In his recently published autobiography, Dear Sir or Madam (Cassell, pounds 11.99), he chronicles his search for employment since graduating with an honours degree in divinity and English in 1979. "My file of job rejections grew and I reached the stage of not wanting to apply for fear of being rejected. There also came a point when acceptance was equally frightening, such was my loss of self-confidence."
Denied a career in the church on graduation because his birth certificate described him as female, Mr Rees has had only casual work for 17 years.
He has now turned to voluntary work and become a borough councillor in Tunbridge Wells. "I leave the job centre two inches high and walk into the council offices as a human being," says Mr Rees.
Many employers are ill-informed about transsexuality. While the issue is covered in blanket terms in equal opportunities policies, few specific procedures are outlined. When a high-level employee at GEC broached the issue back in 1983 the company had no experience of transsexuality. Colleagues backed the employee, and the company supported her during her two-year gender change, giving her time off for surgery.
Since then GEC has employed other transsexuals, but has not adopted a set policy because it believes the circumstances surrounding each case vary.
At British Telecom the issue has worked its way up to central policy level. Twenty two individuals have had a sex change while at BT, all male to female. They come under the wing of the company's health and counselling service, which also advises their colleagues and managers. "It may be difficult for an employee to carry on with his or her job, so we will transfer them if they want," says Peter Archer, employee relations director.
Employees are allowed time off for surgery and on return their names are changed on the company's records.
Dr Stephen Whittle, author of Transvestism, Transsexualism and the Law (Beaumont Trust and Gender Trust, pounds 10) says that the nebulous protection afforded by the law means that "there is every need for an employer to adopt a humane approach".
Dr Whittle, a female-to-male transsexual, continues to push for a fundamental change in the law. He backed a Private Member's Bill from Alex Carlile, Liberal Democrat spokesman on justice, which ran out of time in the Commons in early February.
Mr Carlile favours the introduction of a register that would allow transsexuals to be issued with new birth certificates. Given the support for the Bill from all sides of the House he finds it incomprehensible that his 10-year campaign has not yet succeeded. "The problem is that people know so little about transsexualism," he says. "Ignorance is the enemy."