Theresa May’s draft Brexit deal “threatens the integrity” of the United Kingdom, a veteran Northern Ireland politician has warned.

Democratic Unionist Party peer Lord McCrea of Magherafelt and Cookstown used his maiden speech in the House of Lords, traditionally reserved for uncontroversial issues, to argue the proposed withdrawal agreement would “drive a coach and horses” through the devolution settlement.

Speaking during a lengthy debate in the upper chamber, the former MP insisted that Great Britain and Northern Ireland “must leave the European Union on equal terms” and argued the draft document was “not a good deal” for the UK and should be rejected.

Lord McCrea said: “We are proud to be a part of the United Kingdom but I believe the deal presented by the Prime Minister threatens the integrity of that Union.

“If these proposals were implemented, we in Northern Ireland would have to take rules from a body without any representation, governed by laws which even if they damaged our economy could not be changed and which we have no say in.

“These proposals drive a coach and horses through the devolution settlement and our constitutional practices to suit the European Union.”

Focusing his criticism on the backstop, aimed at avoiding a hard Irish border, the DUP peer said: “The Government claim of a United Kingdom customs solution is simply untrue.

“Northern Ireland will be in the EU customs territory while Great Britain will not.

“If Great Britain were to leave then the EU has the right to impose a customs border.

“Northern Ireland is a hostage to prevent GB leaving or the sacrifice if it does.”

He added: “The hard border is a fictitious problem but based on this fiction Northern Ireland is to be pushed further away from Great Britain.

“For a backstop never to be used it takes up a substantial chunk of the withdrawal agreement.”

Lord McCrea warned: “The people of Northern Ireland have a respect for straight-talking. They do not stand for anyone seeking to pull the wool over their eyes.”

“The United Kingdom of Great Britain and Northern Ireland must leave the European Union on equal terms.

“The present proposals are not a good deal for the United Kingdom and should be rejected and my party – the Democratic Unionist Party –  will do the honourable thing and vote against.”