Reducing the number of NHS nurses could have 'catastrophic consequences' for patient safety and care, the Royal College of Nursing (RCN) warns.
The Chief Executive of the RCN, Dr Peter Carter, said there was evidence to show some hospitals were axing hundreds of nursing posts and that it was a 'myth' the government was protecting frontline staff.
Other hospitals are using less-qualified healthcare assistants instead of nurses in a bid to cut costs, he claimed.
It comes as the union identified almost 40,000 NHS posts across the UK that face being lost over the next three years, up from the 27,000 it reported in November.
Some redundancies could be in the pipeline but most losses are expected to be through natural wastage, such as people not being replaced when they leave or retire, or recruitment freezes.
The RCN, which has been analysing data from more than 130 NHS organisations, revealed the figures on the first day of its annual conference in Liverpool. About 5,000 nurses are gathering at the event to debate key issues.
An in-depth analysis of almost 10,000 job cuts from 21 NHS trusts in England showed 54% (5,209) will be clinical posts, such as nurses and midwives.
Almost half, 4,429 posts, are nurses and healthcare assistants. When workforce planning levels for trusts are compared, 12% of the overall nurse workforce faces the axe.
The RCN said it expects patients to suffer as services such as family nurse partnerships and talking therapies for depression are closed.
Some trusts are shutting key community services like these "with the suggestion that they might start up again in the future", despite minimal evidence this will happen.
Dr Carter said: "Clinical staff are the lifeblood of the NHS and it is haemorrhaging at an alarming rate.
"Many trusts are not being transparent by admitting to the proportion of clinical jobs being lost."