Almost two-thirds of healthcare assistants (HCAs) are performing roles usually undertaken by nurses, such as giving patients drugs and dressing their wounds, in the latest illustration of the NHS’s staffing crisis.

The apparently growing trend of assistants acting as “nurse substitutes” has sparked concern that patients may receive inferior or potentially unsafe care because they do not have the same skills.

Of the 376,000 assistants in the NHS in England, 74% are taking on extra tasks, according to findings by the union Unison.

In a survey of almost 2,000 mainly hospital-based HCAs across the UK, 63% said they were providing patient care with worryingly little help from doctors and nurses, and 39% said they were not confident the patients they look after were receiving safe care.

Q&A Does the UK have enough doctors and nurses? Show The UK has fewer doctors and nurses than many other comparable countries both in Europe and worldwide. According to the Organisation for Economic Co-operation and Development (OECD), Britain comes 24th in a league table of 34 member countries in terms of the number of doctors per capita. Greece, Austria and Norway have the most; the three countries with the fewest are Turkey, Chile and Mexico. Jeremy Hunt, the health secretary, regularly points out that the NHS in England has more doctors and nurses than when the Conservatives came to power in 2010. That is true, although there are now fewer district nurses, mental health nurses and other types of health professionals. NHS unions and health thinktanks point out that rises in NHS staff’s workloads have outstripped the increases in overall staff numbers. Hospital bosses say understaffing is now their number one problem, even ahead of lack of money and pressure to meet exacting NHS-wide performance targets. Hunt has recently acknowledged that, and Health Education England, the NHS’s staffing and training agency, last month published a workforce strategy intended to tackle the problem. Read a full Q&A on the NHS winter crisis

“On my first day I was shown how to do tasks like taking pulses and blood pressures by another HCA,” said Nicole, an HCA in Greater Manchester and Unison member.

One healthcare worker who asked to remain anonymous said: “They said they’d never been trained properly how to do it and weren’t really sure if they were doing it properly. HCAs are doing electrocardiograms and taking bloods. That’s a lot of responsibility.”

In the survey, 51% of HCAs said they had not been properly trained to dress wounds, give out medication or change stoma bags.

“Healthcare assistants are being left to fill staffing gaps and do vital tasks without recognition or reward. It’s bad for them and bad for patients”, said Unison’s head of health, Sara Gorton. “It’s clear the pressures on them to act as nurse substitutes have increased over the winter.”

A majority of respondents (57%) said they had to perform extra tasks last winter as the NHS came under its most intense pressure ever, and 41% said they were asked to act beyond the usual limits of their roles, and without proper training more often than the previous winter.

The creeping expansion of HCAs’ roles, linked to the NHS in England’s shortfall of 40,000 nurses, risks leading to “nursing on the cheap”, the Royal College of Nursing said in response to the findings.

“As the shortage of nurses continues to bite, shifts are increasingly filled with more unregistered care staff,” said the RCN’s general secretary, Janet Davies. “Support workers play an extremely important role, but they should supplement the work of nurses, not replace them.

“It’s unfair on HCAs to expect them to deliver care they have not been trained for. It’s also unfair on patients,” she added. “Health outcomes improve with more registered nurses on duty. The government must not allow nursing on the cheap, and increasing the supply of registered nurses must be a priority.”

Jonathan Ashworth, the shadow health secretary, said: “The situation is getting worse year by year, putting patient safety at risk. It’s totally unacceptable to expect healthcare assistants to fill in, effectively acting up while denying them the training and support they deserve for taking on extra responsibilities.”

The policy director at the Nuffield Trust health thinktank, Candace Imison, said the findings were worrying. She said: “We know that across the NHS, staff – from healthcare assistants to clinicians – are being stretched beyond their capacity daily as the health service grapples with staff shortages and growing numbers of sick and frail patients.”