The Northern Ireland Secretary has insisted the region's voice will still be heard at a key Government Brexit committee despite his omission from its core membership.
James Brokenshire said he is "entirely satisfied" with the arrangement that will only see him invited to attend the European Exit and Trade Committee when permanent members think his presence is required.
The Welsh and Scottish secretaries will also attend on that basis, which has prompted claims from political rivals that the devolved regions are not central to the Government's Brexit planning.
Prime Minister Theresa May will chair the Brexit committee. Its 12 core members include Foreign Secretary Boris Johnson, Brexit Secretary David Davis and Chancellor Philip Hammond.
"I am able to attend meetings of that committee where there are Northern Ireland-related issues," said Mr Brokenshire.
"I am confident I am able to represent Northern Ireland's view, Northern Ireland's perspective, into the Brexit consideration and absolutely remain at the heart of discussions across Whitehall in ensuring the voice of Northern Ireland is heard loud and clear, and I am that champion to ensure that the issues that matter to Northern Ireland are properly reflected into the negotiation."
In an interview with BBC Radio Ulster, he added: "I am entirely satisfied that the arrangements that are in place are appropriate for me to advocate very firmly the views of Northern Ireland and to ensure we do have that loud voice in Whitehall underlining the key themes."
Later, Deputy First Minister Martin McGuinness said he had no faith that the British Government would deliver for Northern Ireland on Brexit.
The Sinn Fein MLA said: "I don't trust this British Government to negotiate on our behalf. They don't have the best interests of the people of the North at heart.
"And despite what James Brokenshire may say, he will not be my representative at those negotiations. That is the responsibility of elected representatives here.
"I represent the 56% of people who voted to remain in the EU. Our democratic wishes need to be listened to and respected."
He is expected to travel to London to meet with the Prime Minister, as well as the Scottish and Welsh First Ministers, to discuss the fallout.
Mr McGuinness added: "Key areas of concern were identified in the joint letter from (First Minister) Arlene Foster and myself and the question is whether the British Government is taking those seriously, and the answer is I don't think so."