The case of two Catholic midwives fighting for the legal right to avoid any involvement in abortion procedures reaches the UK's highest court today.

Mary Doogan and Connie Wood, who are conscientious objectors to the process, were successful at the Court of Session in Edinburgh in April last year.

That victory followed a ruling against them in 2012 in their action against NHS Greater Glasgow and Clyde.

In the latest round of the battle, five Supreme Court justices in London will hear a challenge by the health authority against last year's decision by three appeal judges.

As conscientious objectors, the women have had no direct role in pregnancy terminations.

But the midwifery sisters, who are in their 50s, claim they should also be entitled to refuse to delegate, supervise and support staff involved in the procedures or providing care to patients during the process.

The health board argued that conscientious objection was a right only to refuse to take part in activities that directly brought about the termination of a pregnancy.

In the appeal ruling in favour of the women, Lady Dorrian, with Lords Mackay and McEwan, said: "In our view, the right of conscientious objection extends not only to the actual medical or surgical termination but to the whole process of treatment given for that purpose."

After the decision Ms Doogan and Ms Wood voiced their delight and said the ruling affirmed the rights of all midwives to withdraw from a practice that would ''violate their conscience''.

The women were employed as labour ward co-ordinators at Southern General Hospital in Glasgow. At the time of the original ruling, Ms Doogan had been absent from work due to ill health since March 2010 and Ms Wood had been transferred to other work.

Both registered their conscientious objection to participation in pregnancy terminations years ago, under the Abortion Act, but became concerned when all medical terminations were moved to the labour ward in 2007.

They said being called up to supervise and support staff providing care to women having an abortion would amount to ''participation in treatment'' and would breach their rights under the European Convention on Human Rights.

In the original ruling against them, the judge, Lady Smith, found that the women were sufficiently removed from involvement in pregnancy terminations to afford them appropriate respect for their beliefs.

At the Supreme Court the appeal will concern the scope of the right to conscientious objection under the Abortion Act 1967 and in particular the decision of the appeal judges that the women's entitlement to conscientious objection includes the entitlement to refuse to supervise staff in the provision of care to patients undergoing termination.

The Royal College of Midwives (RCM) and British Pregnancy Advisory Service (bpas) warned of the implications.

Ann Furedi, bpas chief executive, said: "bpas supports the right of healthcare professionals to conscientious objection, not least because women deserve better than being treated with contempt by those who think they are sinners. But ultimately a balance needs to be struck between that exercise of conscience and women's access to legal services.

"There may be a small number of healthcare workers who have a conscientious objection to providing abortion care. There are far more who have a conscientious commitment to helping women who need to end a pregnancy.

"It would be grossly unjust if an interpretation of conscientious objection was allowed to stand which would disrupt services to the point that those committed to helping women were unable to do so."

Gillian Smith, RCM director for Scotland, said: "We absolutely support midwives' rights to conscientious objection. The RCM position has always been and will remain that we support women's choice within the law.

"We also want to ensure that women undergoing this procedure, for whatever reason, get the best possible care, which we feel could be compromised if the current laws are changed.

"Whilst recognising the rights of healthcare professionals to conscientious objection as described in the 1967 Abortion Act, we will be encouraging our members to continue to provide professional care to women who require this type of treatment."