THERESA May was left reeling during a session with business leaders in New York yesterday after a major global investor said Britain’s future was daunting, and asked the Prime Minister to be honest and say how bad Brexit could get.

Steve Schwarzman of asset management firm Blackstone, who last week paid £1.5 billion for thousands of commercial spaces underneath Victorian railway arches in the UK, said he had faith in the British economy “but on the other side, things could really go off with a bad Brexit and also a change of government”.

He added: “The thing that we really worry about is how bad can things get? We believe in the good things. But in terms of just thinking about it from a risk management perspective it’s a little daunting for those of us on the outside.”

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May said: “I absolutely appreciate and understand that – you’re making decisions and looking ahead to what the future holds. And at the moment there is that uncertainty about what the future will hold in terms of Brexit.”

The Prime Minister continued: “First of all … we believe that we will and can get a good deal. And that’s because it’s not just about the UK, it’s about the EU as well. And I think that continued trading relationship is going to be good for both sides.”

However, she admittted there were still “several weeks of intense work to be done” in negotiations.

The difficult question overshadowed a speech to business leaders where May promised that “post-Brexit Britain will be an unequivocally pro-business Britain”.

The Prime Minister told the corporate leaders that businesses coming to Britain would be able to “access service industries and a financial centre in London that are the envy of the world, the best universities, strong institutions, a sound approach to public finance and a consistent and dependable approach to high standards but intelligent regulation”.

But on Tuesday, a survey by the Chartered Institute of Procurement and Supply revealed that delays of just half an hour at UK ports caused by a hard Brexit could potentially lead to one in 10 UK businesses going bankrupt as firms face massive queues and a vast increase in paperwork and checks to clear customs.

SNP MP Peter Grant said he thought the Prime Minister was being “disingenuous”.

“The economic evidence continues to mount against the dangers posed by a Tory hard Brexit, yet Theresa May is intent on pressing down hard on the accelerator as we edge closer to the Brexit cliff edge,” he said.

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“While the Prime Minister delivered her so-called pro-business message in New York, one in 10 firms back home in the UK are facing bankruptcy if the UK crashes out of the EU without a deal, with businesses also facing a mountain of paperwork and checks in order to continue operating.

“Theresa May is guilty of being utterly disingenuous.

“If the Prime Minister is intent on being ‘unequivocally pro-business’ then she must heed the unequivocal calls from the business community that staying in the customs union is vital in order to protect our economy.

“Companies and their workers will need much more than warm words from the Prime Minister given the flippant attitude of her Brexit Secretary who staggeringly claimed that struggling businesses in the UK are choosing to blame Brexit, rather than taking responsibility for their own loss in profits.

“The Tory government’s Chequers proposal is in tatters.”

Grant added: “It has been rejected by the EU, as well as by a sizeable number of the Prime Minister’s own backbenchers – and it’s high time the Tory party ended its hypocritical, narrow-minded and divisive approach to Brexit, and instead worked with the devolved governments, the business community and other organisations, to protect Scotland and the UK’s economy, jobs and living standards.”