Bernadette Cadman, a principal inspector of health and safety, has been fighting for justice after discovering her employer, the Health and Safety Executive, was paying male colleagues on the same grade as her between £5,000 to £7,000 more per year largely as a result of a pay system based on seniority.

In his opinion published today the Advocate General agreed with Cadman that it was unlawful to allow for men in a comparable role to be paid more than their female colleagues solely on the basis of length of service without any need to show why that was justifiable.

Prospect General Secretary Paul Noon said: "We welcome the opinion and are optimistic that the Court’s final verdict, when published, will back the Advocate General’s findings. However, we are disappointed that a time limit is recommended on the submission of further claims from employees facing the same discrimination as our member.

"This is the most important equal pay claim to be brought in the last 10 years and is particularly relevant to public services or any employment where long seniority-based pay scales exist, or where additional contractual benefits are dependent on long service, such as enhanced holiday entitlements.

"When service-related pay is analysed women are often clustered at the lower parts of the pay band. This is because, as demonstrated in evidence provided in this case by the Equal Opportunities Commission, statistically women have on average shorter service due in the main to children or other care responsibilities. The increase of women entrants to traditionally male dominated professions also raises questions over seniority-based pay."

Prospect’s legal team presented the case to the ECJ in March after Cadman was granted leave to appeal an earlier ruling by a UK employment appeal tribunal that challenged the outcome of her initial tribunal case, held in May 2002.