The European Union is “open” to a two-year Brexit delay, chief negotiator Michel Barnier has confirmed.

In a letter to the Westminster leaders of the SNP, Lib Dems, Plaid Cymru, SDLP, Green Party and Alliance Party, Mr Barnier said the option of an extension to the Brexit transition period is available if the UK wants it.

But the UK’s chief negotiator David Frost told MPs the “firm policy” of the Government remains not to extend beyond the end of the year.

The leaders of these parties had written to Mr Barnier on May 15 calling for a two-year extension to be agreed between the UK and the EU amid a negotiation deadlock.

The SNP’s Westminster leader Ian Blackford welcomed the letter and called on Boris Johnson to accept the offer to help protect the economy during the coronavirus pandemic.

The Brexit transition began when the UK legally left the EU on January 31 and is due to conclude at the end of the year.

Mr Frost told the Commons Committee on the Future Relationship with the European Union on Wednesday: “That is the firm policy of the Government, that we will not extend the transition period and if asked we would not agree to it.”

In his letter, Mr Barnier said: “Such an extension of up to one or two years can be agreed jointly by the two parties.

“The European Union has always said that we remain open on this matter.

“Any extension decision has to be taken by the Joint Committee before July 1, and must be accompanied by an agreement on a financial contribution by the United Kingdom.”

Responding to the letter, Mr Blackford said: “Boris Johnson must finally put his responsibilities to jobs, living standards and the economy first, and urgently agree the two-year extension on offer to the transition period.

“It would be madness to pile a Brexit crisis on top of the coronavirus crisis we already face – with unemployment soaring, businesses shedding jobs, and many struggling to survive.

“Time is running out. There is just a month left to agree an extension to prevent the UK crashing out with a devastating bad deal or a catastrophic no-deal.

“If the Prime Minister fails to agree an extension he will be responsible for every job lost, every income slashed, and every business that goes under as a result of his bad Brexit deal.

“The SNP will continue to press for a long extension to protect Scotland’s economy – but the only way to guarantee Scotland’s interests and protect our place at the heart of Europe is to become an independent country.”

Lib Dem leadership candidate Layla Moran urged Mr Johnson to “put his pride aside” and agree to an extension.

She said: “The transition period was designed to give us time to secure a trade deal and make preparations for it to come into effect.

“That time has already, and understandably, been decimated by the coronavirus response. This makes a dangerous no-deal Brexit more likely at the end of the year, unless we extend the transition period.

“I am urging the Prime Minister to put his pride aside, tackle the crisis in front of him and take the extension he’s being offered.”