Serious mistakes by NHS hospital staff including surgical errors, delayed diagnosis, and sub-optimal care for patients with deteriorating conditions have risen sharply, official figures show.
The NHS England statistics, obtained by the Liberal Democrat health spokesman Norman Lamb, showed the number of serious incidents involving sub-optimal care more than doubled to 588 in 2015/16 from 260 two years previously.
Diagnostic incidents, including delayed diagnosis and a failure to act on test results, have jumped more than 40% to 923 last year, compared to 654 in 2013/14.
Surgical errors, which include doctors performing surgery on the wrong part of a patient's body, on the wrong patient or using the wrong procedure, more than doubled last year to 740 incidents recorded as serious enough to require investigation.
Mr Lamb, who uncovered the figures using Freedom of Information laws, demanded extra funding for the health service and criticised the Government's "cavalier" attitude to the financial crisis facing the NHS.
"These figures show a deeply worrying rise in the number of incidents which have a damaging and potentially fatal effect on patients," he said.
"Thousands of people are being failed in their hour of need because the NHS is under such intolerable pressure, with overstretched hospital staff unable to give patients the care and treatment they deserve.
"The Government must stop turning a blind eye to the funding crisis which is stretching our health service to breaking point.
"We must work cross-party to deliver a new long-term financial settlement for the NHS and social care."
Meanwhile, Mr Lamb renewed calls for a 1% tax dedicated to funding health and social care.
He told BBC Radio 4's PM programme: "There's a very strong case for a dedicated tax.
"One of the problems we have, particularly in an age where people have lost trust with politics, politicians, government, they think that just paying extra tax goes into a big black hole and doesn't deliver the services that they see as important.
"If we had a dedicated health and care tax then people could see very clearly on their wage packet the amount that they were paying in to sustain the health and care system."
A Department of Health spokesman said the increase in serious incidents was down to the NHS becoming better at recording mistakes.
The spokesman said: "This data is precisely what we would expect given the Government's focus on building the safest and most transparent healthcare system in the world - the NHS is becoming ?far better at recording and learning from the open reporting of a wider range of incidents.
"To suggest this indicates a decline in standards is a simple misreading of the information."