PM also used his Commons appearance to guarantee rights of EU nationals in the UK

Boris Johnson has reiterated his pledge to ditch the Irish backstop while scaling up preparations for a no-deal Brexit, as he used his first parliamentary outing as prime minister to guarantee the rights of EU nationals in the UK.

Johnson outlined to a noisy Commons his vision of a post-Brexit UK in 2050 as “the greatest and most prosperous economy in Europe at the centre of a new network of trade deals”.

He repeated promises given during the Conservative leadership campaign to seek from the EU the removal of the backstop insurance policy for the Irish border, which Brussels has dismissed as impossible, as part of a new withdrawal agreement.

But under questioning from backbench MPs Johnson was unable to give specifics as to how he could persuade the EU to change its view or what non-backstop arrangements could be used on the Irish border. Instead, he repeatedly accused his critics of lacking optimism.

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“A time limit is not enough,” Johnson said. “If an agreement is to be reached, it must be clearly understood that the way to the deal goes by way of the abolition of the backstop.

“For our part, we are ready to negotiate in good faith an alternative with provisions to ensure that the Irish border issues are dealt with where they should always have been: in the negotiations on the future agreement between the UK and the EU.”

Pledging to pull Britain out of Europe on 31 October, Johnson said he had told Michael Gove, who has the non-portfolio cabinet role of chancellor of the duchy of Lancaster, to focus on preparing for a no-deal Brexit.

“I have today instructed the chancellor of the duchy of Lancaster to make these preparations his top priority,” he said. “I have asked the cabinet secretary to mobilise the civil service to deliver this outcome should it become necessary. And the chancellor has confirmed that all necessary funding will be made available.”

On EU nationals, Johnson said he wanted to “repeat unequivocally our guarantee to the 3.2 million EU nationals now living and working among us”. He said: “I thank them for their contribution to our society and for their patience, and I can assure them that under this government they will have the absolute certainty for the right to live and remain.”

Q&A Who sits in Boris Johnson's first cabinet? Show Hide The following people are in Boris Johnson's first cabinet: Sajid Javid, chancellor

Dominic Raab, foreign secretary

Priti Patel, home secretary

Michael Gove, chancellor of the Duchy of Lancaster

Robert Buckland QC, lord chancellor and justice secretary

Stephen Barclay, Brexit secretary

Ben Wallace, defence secretary

Matthew Hancock, health secretary

Andrea Leadsom, business secretary

Liz Truss, international trade secretary

Amber Rudd, work and pensions secretary

Gavin Williamson, education secretary

Theresa Villiers, environment secretary

Robert Jenrick, housing secretary

Grant Shapps, transport secretary

Julian Smith, Northern Ireland secretary

Alister Jack, Scotland secretary

Alun Cairns, Wales secretary

Baroness Evans, leader of the House of Lords

Nicky Morgan, DCMS secretary

Alok Sharma, international development secretary

James Cleverly, party chair and minister without portfolio These people also attend full cabinet meetings: Rishi Sunak, chief secretary to the Treasury

Jacob Rees-Mogg, leader of the House of Commons

Mark Spencer, chief whip

Geoffrey Cox QC, attorney general

Kwasai Kwarteng, energy minister

Oliver Dowden, paymaster general and minister for the Cabinet Office

Jake Berry, minister of state at the Cabinet Office

Esther McVey, housing minister

Jo Johnson, universities minister

Brandon Lewis, security minister

Responding to Johnson, Labour said the new PM had inherited “a country that’s been held back by nine years of austerity, that has hit children and young people the hardest”.

The Labour leader, Jeremy Corbyn, said: “No one underestimates this country. But the country is deeply worried that the new prime minister is overestimating himself.”

Johnson said in his speech, loudly cheered by many Tory MPs, that all members of his new cabinet were committed to leaving the EU on 31 October “whatever the circumstances – and to do otherwise would cause a catastrophic loss of confidence in our political system”.

He said: “It would leave the British people wondering whether their politicians could ever be trusted again to follow a clear democratic instruction. I would prefer us to leave the EU with a deal. I would much prefer it. I believe that it is possible even at this late stage, and I will work flat-out to make it happen. But certain things need to be clear. The withdrawal agreement negotiated by my predecessor has been three times rejected by this house. Its terms are unacceptable to this parliament and to this country.”

Johnson seemed to struggle to answer questions on specifics of the new approach to Brexit. He was asked by Labour’s Hilary Benn what he would do, given that the Irish prime minister, Leo Varadkar, had ruled out a new withdrawal agreement while the Commons seemed likely to block no-deal Brexit.

Johnson responded: “I think what the right honourable gentleman has said is redolent of the kind of defeatism and negativity that we’ve had over the last three years. Why begin by assuming that our EU friends will not wish to compromise?”

Similarly, when another Labour backbencher, Yvette Cooper, asked Johnson about what practical solutions could be used for the Irish border in the absence of a trade deal or backstop, he replied that were “abundant facilitations already available”.