The company is to appeal the case to the Supreme Court after the High Court found that six contract meter readers were fully employed and not "contractors providing services".

The judgement, which upheld an earlier finding by the Department of Social Affairs' Appeals Tribunal, now opens the way for over 300 meter readers to be treated as employees of the ESB and raises the prospect of the company having to reimburse these workers for holiday pay, sick leave and pension contributions dating back to 1994. Sources say the cost of such back payments would be "many millions".

Delivering his judgement, Justice Gilligan said that "in general, a person will be regarded as providing his or her services under a contract of service, and not as an independent contractor, where the person is performing the services for another person and not himself."

Brendan Ogle, regional industrial organiser for the ATGWU which has been fighting the case since 2002, said the judgement, if upheld, would "feed into the wider market debate around the issue of job degradation and the use of contracts by employers as a convenience".

The judgement "assists workers everywhere who are treated as contractors simply for convenience, financial or revenue reasons", Ogle said, adding that it would "aid employee representatives in ensuring that workers get the proper protections they are entitled to under legislation.

Annual leave, pensions, holiday pay, sick pay and other conditions can all be more effectively addressed as a result of this judgement."

Although the men's contracts specifically stated that the meter reader was "an independent contractor and shall not be an employee of the ESB", the case turned on a decision by ESB to provide meter readers with a portable computer and the company's insistence that meter readers, and anyone substituting for them, must carry an ESB ID card. This had not been the case in earlier unsuccessful appeals by meter readers. "The details before me suggest very strongly that they are in fact in a master/servant relationship with the ESB, and I therefore consider that they are engaged under a contract of service, " the judge said, adding that he considered that "this has been the position since the introduction" of the hand-held computer in 1994.