Tens of thousands of people facing long waits for NHS care could be eligible to travel abroad for treatment and be reimbursed for the cost, after a landmark judgment yesterday.

In a High Court case involving a woman who went to France for a hip replacement, Mr Justice Munby ruled that patients facing "undue delay" because of long NHS waiting lists were entitled under European law to obtain funding for overseas treatment.

The judge said what constituted undue delay would vary from case to case and depend on factors including pain, suffering and immobility.

He said that in the case of Yvonne Watts, a 72-year-old grandmother who was in pain with osteoarthritis, it was "very much less" than a year but "significantly, though probably not substantially, more" than three months.

Figures show 178,500 people waiting more than six months for treatment on the NHS and 49,000 waiting more than nine months. A spokesman for the Department of Health, which has a scheme for sending patients abroad when waiting lists are long, said: "This is a complex case and we need to consider the detail. We are looking at any wider implications for the NHS."

Liam Fox, the shadow Health Secretary, said the case highlighted "confusion and disarray" in the Government. He said: "The judgment shows what happens when it is unclear to patients the extent of treatment to which they are entitled overseas."

Mrs Watts had sought reimbursement for the £3,800 cost of her operation from Bedford Primary Care Trust. She had been told last year that the waiting list for treatment was 15 months but she had shortened that time by paying for a private consultation and putting pressure on the hospital. In February this year she was offered an appointment for the operation on 6 May but she chose instead to travel to St Isabelle Hospital in Abbeville, Normandy, where she had her right hip replaced on 7 March. The trust had rejected her request for authorisation to go abroad because, it said, it was not necessary as the trust was meeting the Government's maximum waiting time of 15 months for in-patient treatment.

Dismissing that argument, Mr Justice Munby said Mrs Watts had won her case "in principle". But he rejected her claim for a refund of £3,800 because on the date set for the case ­ 4 February this year ­ she had faced a delay of three months until the operation date she had been offered of 6 May. He said undue delay in her case would have been "a period very much less than the year with which the claimant was originally faced, but on the other hand a period significantly, though probably not substantially, greater than the period of delay until April or May 2003 with which she was faced. On that simple ground, as it seems to me the claimant's case breaks down."

Mrs Watts' solicitor, Richard Stein, said: "This judgment is a very good one for patients. A good proportion of the 180,000 patients waiting longer than six months for treatment ought to be looking at this judgement for how it might affect them."

Gill Morgan, chief executive of the NHS Confederation, said few patients were likely to take advantage of the ruling, which was the first interpretation by a British judge of an earlier European Court of Justice ruling in a Dutch case.

She said: "The numbers affected could be large but patients will have to find a hospital abroad to be treated in, make the arrangements and then send the bill to their local trust. Not many are likely to do that because it is complicated."

Julie Harding, Mrs Watts' daughter, said her mother, who was not in court, was very pleased with the judgment. She said: "We have established that the primary care trust was wrong in law to simply use waiting lists as a reason to refuse my mother permission to go abroad for her operation."

She added that her mother was now well. "She has got her life back," she said.