By Andy Verity BBC Economics correspondent
That's according to research published today, which suggests that between 800,000 and a million businesses nationwide may soon have to close.
Many firms have told the BBC that banks have refused them emergency loans.
Others can't get through on the phone or were told the money will take weeks.
The banks say they are following the rules set out by the government.
Chancellor Rishi Sunak said two weeks ago that businesses would be able to walk into bank branches and discuss Coronavirus Business Interruption loans of up to £5m to help them survive the shutdown.
The promise from the chancellor was that "any good business in financial difficulty who needs access to cash to pay their rent, the salaries of their employees, pay suppliers, or purchase stock, will be able to access a government-backed loan, on attractive terms".
However, thousands of struggling firms can't get through to their banks by phone or, when they do, are being told by the banks they're not eligible.
And Mayor of London Sadiq Khan has told BBC Radio 5 Live that 'banks have got to step up' to help small and medium-sized businesses survive during the
Steve Lord runs Belgrave & Powell, a Nottingham-based engineering group employing 120 people and supplying services to customers such as BAE's Samlesbury site, where the F-35 and Typhoon fighter jets are made.
'Disappointment after disappointment'Since Salmesbury halted production, his business - like millions of others - is facing the prospect of cash drying up, threatening its ability to pay wages and stay afloat.
"I was heartened and astonished to see the unprecedented help that was announced by the government two weeks ago," he said. "But we put one of our most senior people on it and as each day passed it was disappointment after disappointment."
He said some of the approved lenders were demanding interest rates of up to 30%, which Mr Lord believes is "taking advantage of the situation". Meanwhile, he said, High Street banks were charging around 7%,
Mr Lord thinks too much control has been handed to the banks and approved lenders: "The government needs to make it so everyone's offering the same terms."
"It seems to be that if you are lucky you are banking with the right party, if you're not lucky you'll end up having to close your business."
'The loans won't help'Another business owner, Peter Jackson - who runs
"I thought the whole point of the loans was to help business like mine stay afloat," he said. "But they're not going to help."
The figures identifying how many businesses would not be able to access cash come from a network of accountants serving more than 12,000 small and medium-sized businesses across the country.
Businesses wanting to borrow more than £250,000 are being told by
Joshua Wade runs a fast-growing ethical cosmetics business, Skin and Tonic. He said lenders were insisting on early repayment penalties as well as personal guarantees.
"The Business Interruption Loan Scheme is, in principle, very welcome support right now," he said.
"But the huge barrier for us is the requirement for all directors to give personal guarantees. As founders and executive directors, we already are risking everything but we simply can't ask our non-executive directors to take that risk
A spokesperson for UK Finance, the bank trade body, said: "Lenders are working hard to get financing to all businesses who need it as quickly as possible and are using the Coronavirus Business Interruption Loan Scheme (CBILS) where appropriate, with some funding having already been provided under the scheme.
"All lenders will take into account a business's individual circumstances when considering applications and many business loans can be provided either unsecured or secured on business assets."
Kirsty McGregor, founder of the Corporate Finance Network, told the BBC: "Small and medium-sized businesses employing less than 250 people employ most of the workforce - 23 million people.
"We could lose up to a million of them in the next month or so. And it will be
Ms McGregor suggested the government needs to encourage small businesses to take over companies going bust in their area so employees can still be paid.