Arlene Foster has praised the Prime Minister for “standing firm” against the European Union.

The Democratic Unionist Party leader also warned the European Union to “stop misusing the Northern Ireland peace process as some form of leverage”.

But Sinn Fein President Mary-Lou McDonald dismissed Mrs. May’s words on Friday as “tired rhetoric”.

Theresa May issued a tough statement to the EU on Friday following the summit in Salzburg where European leaders rejected her Chequers deal.

Speaking from Downing Street, Mrs. May said the EU’s dismissal of her Chequers plan without an explanation was “not acceptable” and demanded “respect” for the UK from Brussels.

Mrs. May insisted that Brussels’s “backstop” proposal to keep Northern Ireland in the EU customs area unless a better solution can be found was “unacceptable” to Britain because it would create a customs Border down the Irish Sea.

Her new alternative would “preserve the integrity of the UK” while delivering on a commitment not to establish new regulatory barriers with the rest of the UK without the agreement of the Executive and Assembly in Belfast.

Mrs. Foster said Mrs. May is right to “stand firm in the face of disrespectful, intransigent and disgraceful behaviour by the European Union”.

“The United Kingdom will not be treated in such a manner,” she said.

“I welcome today’s clear statement by the Prime Minister and in particular that Her Majesty’s Government will not countenance any new regulatory or customs barriers between Northern Ireland and the rest of the United Kingdom.”

Mrs. Foster also repeated her warning that her party will veto any “attempt to undermine the economic or constitutional integrity of the United Kingdom”.

“Our red line from day one of these negotiations has been that there can be no border between Northern Ireland and Great Britain,” she said.

“We continue our intensive work with the Government to ensure that we leave the EU in a manner which protects the constitutional and economic integrity of United Kingdom and enables us to take back control of our laws, borders and money.

“The focus by the European Union on the Border between Northern Ireland and the Republic of Ireland is misplaced.

“A currency, VAT and excise Border already exists and is easily managed.

“The European Union needs to stop misusing the Northern Ireland peace process as some form of leverage.”

But Sinn Fein President Mary-Lou McDonald gave a very different reaction, accusing Mrs May of “deflection”.

“Theresa May made a statement today which was billed as a major one in respect of Brexit negotiations. It was, regrettably, no more than an exercise in tired rhetoric,” she said.

“Rather than accepting that her so-called ‘Chequers Plan’ fails to resolve fundamental issues, Theresa May has engaged in deflection.

“Her focus has unfortunately remained on infighting within her own party and her pact with the DUP, instead of coming to an acceptable negotiating position.”