The government has promised to recruit thousands more NHS mental health workers to treat an extra million patients by 2020, but nurses remain sceptical about the proposal, accusing it of lacking detail and questioning how quickly new skilled staff would be signed up.

Recent data revealed that thousands of nursing posts remain unfilled. Figures released by NHS Digital showed that the number of vacancies in the nursing workforce have soared by 15.8% over the last year, confirming the recent disclosure from the Nursing and Midwifery Council that more nurses are leaving the profession than joining it.

Health Secretary Jeremy Hunt said 21,000 new posts would be created under the £1.3bn plan in a bid to end the "historic imbalance" between mental and physical health services. Most of the money would be invested in child and adolescent services and addressing the high dropout rate among trainees.

But the Royal College of Nursing (RCN) warned that the policies "appear not to add up" and said that the government would need to provide more "hard cash" to ensure that the new nurses were trained by 2020.

"It is clear the government will need to work hard just to get back to the number of specialist staff working in mental health services in 2010," said Janet Davies, chief executive of the RCN. "Under this government, there are 5,000 fewer mental health nurses and that goes some way to explaining why patients are being failed. The NHS needs to see hard cash to deliver any plans."

She added that the new report was "unable to provide detail on how the ambitions will be met".

Labour's shadow minister for mental health, Barbara Keeley, was also critical of the proposal, commenting that the government was "promising only jam tomorrow, when what is needed is action today".

Paul Farmer, chief executive of mental health charity Mind, welcomed the government's plan but warned that a "longer-term, further-reaching strategy" was needed to address the "significant gulf between what's in place and what's needed to deliver good quality care".

"A damaging lack of foresight in workforce planning in the past has led us to where we are now. Cuts to mental health services in recent years have led directly to posts being axed and taken its toll on morale, which has led to valued staff leaving mental health in frustration or burn-out," he said.

"It's important to see a focus on the mental well being of the workforce, not least because only when staff are well-supported by their employer can they do their best. Looking after staff also helps retain good people and improve the stability of the workforce in the long run," Farmer added.

NHS nurses protest
Student nurses and health workers take part in a demonstration against government plans to scrap the NHS bursary on 9 January 2016 in London, England Carl Court/Getty Images