Boris Johnson has promised to take Britain into a post-Brexit “golden age” as he clashed with Brussels over his demand that it scrap the Irish backstop.

The Prime Minister told MPs he would work “flat out” to secure a new agreement on Britain's withdrawal from the EU and urged the bloc to rethink its opposition to changing it.

But he quickly ran into a Brussels brick wall. Jean-Claude Juncker, the outgoing European Commission President, in a phone-call to congratulate Mr Johnson on his new role, insisted the existing deal was “the best and only agreement possible” and made clear the bloc would not give in to his demand to renegotiate.

Downing St said the PM had told Mr Juncker he would be “energetic in pursuit of finding a way forward”.

READ MORE: Will Boris Johnson in Number 10 be the catalyst for indyref2?

A spokesman added: “The PM said if an agreement is to be reached, it must be understood the way to a deal goes by way of the abolition of the backstop. The PM and the President agreed to stay in contact."

But Michel Barnier, the EU27’s chief negotiator, also rejected Mr Johnson’s "unacceptable" call for the removal of the Irish backstop and rebuked him for adopting a "combative" approach.

Leo Varadkar, the Taoiseach, stressed the backstop was an “integral part” of the Withdrawal Agreement and without it there was “no withdrawal agreement…no transition phase…no implementation phase and…no free trade agreement”.

The Irish premier added: "So, I hope the new UK Prime Minister has not chosen no-deal; but that will be up to them."

As the new PM faces hostility on one front, he is likely to face it on another when he is expected to travel to Scotland next week for his first meeting with Nicola Sturgeon.

The First Minister has written to him to say it would be “unconscionable” for the UK Government to contemplate a chaotic no-deal exit, which could cost 100,000 Scottish jobs. Downing St said Mr Johnson would respond in due course.

During his first trip to Scotland as PM, he is also expected to meet Ruth Davidson. The Scottish Conservative leader does not see eye to eye with Mr Johnson on Brexit and was accused by the SNP of being “humiliated” when the PM sacked her close colleague David Mundell from his Cabinet post.

One Tory MP has quipped: “Who will give him the warmer welcome; Ruth or Nicola?”

Today, Mr Johnson, on a visit to the Midlands, will launch a police recruitment drive as part of his commitment to put 20,000 more police officers on the beat in England.

No 10 said the “unprecedented drive to deliver more frontline officers” would begin in September.

“My job as Prime Minister is to make our streets safer. People want to see more officers in their neighbourhoods, protecting the public and cutting crime. I promised 20,000 extra officers and that recruitment will now start in earnest,” declared the PM.

Mr Johnson is also expected to make a keynote speech during a trip to northern England on Saturday.

READ MORE: Boris Johnson urges Brussels to drop its opposition to new Brexit deal

Less than 24 hours after becoming the new PM and his dramatic cull of the May Cabinet, which saw 17 ministers depart, Mr Johnson chaired the first meeting of his new-look team and set out his priorities in a Commons statement.

His primary one is to deliver Brexit by the October 31 deadline and he warned of a "catastrophic" loss of confidence in the UK's democracy if Westminster failed.

After entering the Commons chamber to a wave of cheers from Tory backbenchers, their new leader said he much preferred to get a deal and would “work flat out to make it happen”.

“But,” he stressed, “certain things need to be clear.”

The Herald: Camley's cartoon: Boris is PM!Camley's cartoon: Boris is PM!

Noting how the Withdrawal Agreement had been three times rejected by MPs, the PM said: “No country that values its independence and indeed its self-respect could agree to a treaty, which signed away our economic independence and self-government as this backstop does. A time-limit is not enough. If an agreement is to be reached, it must be clearly understood the way to the deal goes by way of the abolition of the backstop.

“For our part, we will throw ourselves into these negotiations with the greatest energy and determination and in the spirit of friendship.

“And I hope that the EU will be equally ready and that they will rethink their current refusal to make any changes to the Withdrawal Agreement.”

The PM explained that if the bloc refused, then there would be no deal.

“In the 98 days that remain to us we must turbo-charge our preparations to make sure that there is as little disruption as possible to our national life,” he said.

In his statement, Mr Johnson pledged to provide an "absolute certainty of the right to live and remain" for the three million EU citizens living in the UK.

But as MPs called for the guarantee to be written into law, No 10 disputed whether this was necessary.

The 3million group, which campaigns on behalf of EU citizens in Britain, branded the PM’s offer a "damp squib”.

The PM also:

*appeared to back an amnesty for up to 500,000 undocumented migrants in Britain while Downing St suggested the Johnson Government had abandoned the controversial target of getting annual net migration below 100,000 a year;

*insisted the NHS was not for sale in any trade deal with the US and

*hinted he might change Government policy in favour of a third runway at Heathrow Airport.

Mr Johnson added that when people in 2050 looked back on this “extraordinary period,” they would be able to say it was the “beginning of a new golden age for our United Kingdom”.

Jeremy Corbyn warned the PM was overestimating the ability of his "hastily thrown-together...hard-right Cabinet" to deliver a new Brexit deal.

"No-one underestimates this country but the country is deeply worried that the new Prime Minister overestimates himself," declared the Labour leader, who last night took part in an anti-Johnson rally in Westminster.

He told MPs: "People do not trust this Prime Minister to make the right choices for the majority of the people in this country when he's also promising tax giveaways to the richest of big business - his own party's funders."

However Mr Johnson drew cheers from Tory MPs with an attack on the Labour leader, accusing the "long-standing Euro-sceptic" of "metamorphosing" into a Remainer.

“The reality now is: we are the party of the people; we are the party of the many and they are the party of the few,” declared the PM.

The SNP’s Ian Blackford quipped Mr Johnson would be the “last Prime Minister of the United Kingdom” and urged him to do the “honourable thing; call a general election and let the people of Scotland have their say”.

But the PM brushed off the call, telling the Nationalist leader: "The people of this country have voted in 2015, 2016, 2017; what they want to see is this Parliament delivering on the mandate they gave us, including him."

Last night, Mr Johnson continued to promote Brexit allies with the appointment of ministers of state, including Kit Malthouse at the Home Office and George Eustice at Environment. But Steve Baker, the leading Brexiteer, turned down a job, saying he did not want to repeat his "experience of powerlessness" as a junior minister yet stressed he had "total confidence" the PM would take Britain out of the EU on October 31.

Junior ministerial appointments will be announced today.