The last Catholic adoption agency in the UK will take its case to the High Court this week to fight equality legislation forcing it to accept gay couples.

Catholic Care, which serves Leeds, Middlesbrough and Hallam in South Yorkshire, will appeal against a Charities Commission ruling which said it could not discriminate against gay would-be parents.

All other Catholic adoption agencies have closed or cut their ties with the church since the Sexual Orientation Regulations 2007 came into power. They were given a two-year window in which to comply with the law.

Catholic Care has said that closing or transferring its adoption activity to other charities are not acceptable options.

Yesterday, bishops for the three areas said that children would “suffer” if Catholic Care was forced to close. The agencies have typically worked to find homes for the children with the most troubled histories.

A letter from Bishop Arthur Roche of Leeds, Bishop Terry Drainey of Middlesbrough and Bishop John Rawsthorne of Hallam said that they believed the adoption agency’s position to be “legally justifiable”.

The letter, read out in churches, said: “Despite the fact that Catholic Care has been able to find caring families for a vast number of needy children we are being invited either to stop our adoption work or stop being a Catholic charity altogether.

“Our position is that it is in the interests of children to continue our work. We are not judging other agencies that accept same sex couples for adoption, but feel strongly that we should not be forced to do so, nor is there a necessity for this to happen.

“We believe that this is a legally justifiable position to take and that it is a reasonable response to a legitimate end.”

Catholic Care had wanted to take advantage of a clause in the Sexual Orientation Regulations which allows charities to discriminate by amending their charitable objectives.

However it was barred from doing so by the Charities Commission.

The High Court will have to consider the correct interpretation of the rules around amending charitable objectives.