Sinn Fein Minister Conor Murphy has effectively snubbed First Minister Peter Robinson in the row threatening the Executive with potential High Court action.

Mr Murphy has written to anti-deal MEP Jim Allister defending his handling of a major policy programme over which Mr Robinson accused the Minister of attempting to “subvert” the Executive and breaking his code of office.

But while the Regional Development Minister has replied to the former senior DUP MEP, he has yet to write to Mr Robinson, who had demanded an “urgent” response.

Mr Murphy’s department confirmed the Minister is still “considering” the letter from Mr Robinson, written two weeks ago, which said the issue “goes right to the heart” of the credibility of the Executive.

At the centre of the row is the Regional Development Strategy for Northern Ireland with Mr Murphy accused of making 157 changes to documents after they were agreed by the Executive, including referring to ‘the North’ and the city of Londonderry as ‘Derry’.

As revealed in the Belfast Telegraph, DUP leader Mr Robinson told him: “I have sought and received legal advice on this and consider you to be in clear breach of our Ministerial duties and that you have acted unlawfully.”

Mr Murphy has made no public comment, but Sinn Fein regards the letter from Mr Robinson as lacking the authority of the First Minister without the co-signature of Deputy First Minister Martin McGuinness, who has also refused to accede to an emergency Executive meeting over the issue.

In a new letter to Mr Allister, Mr Murphy confirmed the first five-year focussed review of the Regional Development Strategy “was developed and published under my Ministerial direction.”

The MEP said Mr Robinson is now facing a major challenge but the DUP said it would not take lectures from Mr Allister.