The number of mental health nurses in England has slumped by more than a tenth over the past decade, new figures have revealed. This is despite commitments from both Theresa May and her predecessor, David Cameron, to boost resources for mental health services, which many medical professionals say are now in crisis.

The total mental health nursing workforce has decreased by 10.6% since 2009, according to the Royal College of Nursing (RCN).

While numbers of mental health nurses have grown in some areas, such as community care, they have fallen elsewhere. Numbers are down by a quarter (25.9%) in acute care and inpatient care – where the number of mental health nurses has fallen by more than 6,000 over the decade.

Donna Kinnair, appointed as RCN chief executive and general secretary last month, will use a speech to the group’s annual congress on Monday to call on ministers to address England’s 40,000 nursing vacancies, and point out the new figures on the reduction in specialist mental health nurses.

“Thousands of experienced professionals have been lost in recent years as the investment failed to match the rhetoric,” she will say. “The shortage of beds, too, leaves vulnerable people often sent hundreds of miles from home and their loved ones for the care they need. As a country and a health service, we are letting down people who must be able to rely on us most. We must draw a line under this and allocate serious resources to mental health care, including the right number of staff.”

Senior medics are also warning privately of frontline problems in some areas. Some hospitals have had to temporarily close beds because of staff shortages, with some wards threatened with closure.

There have already been warnings of a postcode lottery, with some regions having little more than half the resources of the best-funded. According to research from the charity Mind, the average annual spend on mental health services per head of population is £124.48 in parts of Surrey, compared with £220.63 in South Yorkshire.

A drive to recruit more mental health specialists as part of the long-term NHS plan announced earlier this year supports premiums for undergraduates studying the subject or learning disability nursing. The scheme targets mature students and aims to have an additional 4,000 people in training by 2023-24.

Department of Health officials said they were aware of the challenges involved in recruiting the numbers needed to meet targets for improving mental health care. Applications for nursing degree courses have plummeted by 32% since bursaries were scrapped in England in 2016.

The RCN figures demonstrate the continuing pressures on the NHS. There are also complaints that major delays to government plans to tackle adult social care are adding to those pressures. According to information released to Labour under the Freedom of Information Act, more than 28,000 people are sent into residential care away from their home area every year – in one case a person was more than 500 miles from their home authority. The research found that working age adults are disproportionately likely to be sent away for care, with more than one in three being in a care home outside their home area.

A department spokesperson said: “Expanding the mental health workforce across the NHS is a key priority and we’re committed to recruiting and retaining nurses – part of our plan to transform mental health provision with an additional £2.3bn a year investment as set out in the NHS Long Term Plan.

“We’re supporting students to embark on more flexible undergraduate degrees in mental health or learning disability training with an ambition of an extra 4,000 people in training in five years’ time.”