BORIS Johnson’s £1.8 billion cash injection for the NHS in England has been widely criticised as “a drop in the ocean”.

Experts are now calling for more funding to be committed across the health system.

The Prime Minister announced yesterday that much of the one-off payment would go to repairing 20 hospitals as he pledged on his first day in office. But experts said the sum is just a fraction of what is required to fix ailing NHS buildings across England.

Politicians warned that his No-Deal Brexit stance would jeopardise his spending ability, with Labour saying such a departure from the EU will “put lives at risk”.

The announcement prompted nurses, charities and health think tanks to call for additional funding.

Johnson said he is “determined to deliver” the promises of the Brexit referendum campaign, as he announced the sum equivalent to roughly £3.5 million a week to be paid this year. He has received continued criticism for his claim during the EU referendum campaign that leaving the bloc would allow the UK to take back control of £350m a week, with some boosting the NHS.

Of the latest pledge, £850m will go towards funding the vital upgrades to the 20 hospitals. But Ben Gershlick, from the Health Foundation charity, said that “years of under-investment in the NHS’s infrastructure means this extra money risks being little more than a drop in the ocean”.

He warned that NHS facilities are “in major disrepair” in England, with a maintenance backlog of more than £6bn, a figure also cited by other experts.

The chief executive at the Nuffield Trust health think tank, Nigel Edwards, said the sum “will only be a fraction of what it would cost to really upgrade 20 hospitals”.

“Nobody should expect shiny new hospitals in their towns any time soon,” he added.

In an article in The Sunday Times, Johnson acknowledged his ability to spend the cash was based on the economy’s strength.

Critics pointed out that the dire warnings over the effect on finances that a No-Deal Brexit would bring could jeopardise the NHS.

Shadow health secretary Jonathan Ashworth said No Deal would be “a catastrophe” for the health service, particularly if it occurs by the October 31 deadline and ahead of the winter squeeze.

“It will put lives at risk. That is the gamble that Boris Johnson is taking this October, November,” the Labour MP said, appearing on Sky’s Sophy Ridge On Sunday.

Royal College of Nursing chief executive Dame Donna Kinnair said the funding would be backed by colleagues “who have to work in cramped and outdated conditions”.

“However, after this announcement, nursing staff will look to the Prime Minister with even greater expectation of addressing the workforce crisis,” she said.

Dame Donna called for at least an extra £1b yearly to attract new nurses into education, while the Alzheimer’s Society policy director Sally Copley said they were “disappointed that social care is once again playing second fiddle”.

“We urge the Prime Minister to provide an NHS dementia fund to end the injustice people with dementia face today,” she added.

Johnson has threatened a No Deal departure as part of his “do-or-die” commitment by the Halloween deadline. This is despite the Government’s spending watchdog, the Office for Budget Responsibility, warning no deal would increase borrowing by £30bn a year and plunge the nation into recession.

LibDem health spokeswoman Baroness Jolly said Johnson’s pledge “will not be worth the paper it’s written on” when a No Deal hits.

Cancer Research UK policy director Emma Greenwood said the investment would go “some way to address the immense strain” the NHS is under but stressed that funding in recruitment and training is essential to meet rising demand.

Johnson is expected to visit a hospital to announce the new funding. His pledge will add to Theresa May’s £33.9bn annual increase for the NHS by 2023/24.