The European Court of Justice has declared that a directive banning discrimination in the workplace on grounds of disability not only applies to disabled people but also their carers.

The groundbreaking ruling effectively gives new rights to millions of carers across the country. It was made in the case of Sharon Coleman, who claimed she suffered "discrimination by association" after being denied time off from her job as a legal secretary to look after her disabled son.

Her case, which was backed by the Equality and Human Rights Commission, could now result in a huge extension in flexible and part-time working.

But business chiefs have warned that it will create difficulties for employers when balancing the needs of carers of the disabled with those of other parents or carers.

Ms Coleman, 42, from south London, took legal action after claiming she was forced to leave her law firm job because she was not allowed as much flexibility in her work as parents of other children.

She was already working for Attridge Law when she gave birth to a disabled son in 2002. He suffers from serious respiratory problems.

As primary carer Ms Coleman wanted flexible working arrangements. She eventually accepted voluntary redundancy in March 2005 and began a claim for constructive dismissal five months later.

An employment tribunal hearing the case referred it to the European Court for a ruling on whether EU discrimination laws covering disabled people could also apply to someone who was associated with a disabled person.

Judges in Luxembourg have ruled that EU law should protect an employee who has suffered discrimination on grounds of their child's disability.

Employment barrister Ed Williams, of law firm Cloisters, said: "The significance of this ruling cannot be overstated.

"There are literally millions of carers in Britain and the rest of the EU who now have greater protection against discrimination.

"Since the European Directive covers many other areas of discrimination, this ruling clarifies that the protection against associative discrimination ought to apply to the areas of religion or belief, age and sexual orientation as well."

Ms Coleman said: "All I was ever asking for was an equal playing field with the same flexibility afforded to my colleagues without disabled children.

"This has been a long, hard battle and it is not over yet, but I am thrilled that the European Court has ruled in my favour."

The next hearing of her tribunal is expected later this year, when it will decide if she suffered discrimination.

The ruling was welcomed by TUC general secretary Brendan Barber who hailed it as a victory for all parents and carers who look after disabled people.

The director general of Age Concern, Gordon Lishman, said: "This is a huge win for carers in Britain. It will not only help to protect parents providing care but could also have implications for the ever-increasing number of people in the UK providing care to an older relative."

But the deputy director-general of the Confederation of British Industry, John Cridland, said: "This appears to be a significant new employment right for the carers of the disabled, and will leave employers in difficulty when prioritising flexible working between carers of disabled people, and other carers and parents."