The NHS will offer mature students a £5,000 bonus to become mental health or learning disability nurses as part of its forthcoming long term plan, the Guardian can reveal.

The payments are designed to tackle severe nursing shortages in two areas that NHS bosses and ministers have agreed are key priorities in which care needs to be significantly improved.

Mature students, likely to be those aged over 25, will qualify for the money if they agree to specialise as nurses dealing with either of those types of patients. NHS officials hope the payments, which will be called “earn and learn support premiums”, will boost recruitment.

“Improving care for people with mental health conditions and learning disabilities are absolute priorities in the long term plan so it makes sense that we try and incentivise people – mature candidates – to train as nurses in those areas”, said one official.

Applications for undergraduate degree courses in nursing have plummeted by 32% since bursaries for student nurses were scrapped in England in 2016, despite warnings that the move would backfire. Applications from mature students to study mental health and disability nursing fell even more sharply – by 40% – between 2016 and this year. Interest has dwindled so dramatically that many universities are considering axing their specialist courses.

The new incentive scheme will be included in the plan, which will set out how the NHS in England will spend the £20.5bn annual budget increase Theresa May has promised it by 2023. Its publication was due this week but that has been delayed until January due to the government’s paralysis over Brexit and further recent disagreements between NHS England and ministers over how ambitious the plan will be, especially how quickly the service can start delivering key waiting time targets covering A&E treatment, cancer care and planned operations in hospital.

However, one NHS hospital trust boss said the £5,000 payments were likely to do little to address the critical shortages of both types of nurses and would prove “a drop in the ocean”. The NHS in England is short of 42,000 nurses, official figures show.

“On the face of it, I’m sure this can be painted as positive news, as anything that is done to reverse the significant cuts to some areas of nursing, which certainly include mental health and learning disabilities, is critical”, said David Munday, the trade union Unite’s lead officer for mental health who is also head of the Mental Health Nurses Association.

But both Munday and the Royal College of Nursing (RCN) questioned whether the new payments may prove to be a watered-down version of a scheme the Department of Health and Social Care announced in May under which mature students agreeing to becoming district, mental health or learning disabilities nurses would receive £10,000. It has not disclosed any further details since then or announced a start date for it.

“It’s very hard to understand whether this new plan for £5,000 payments is actually a 50% cut in a previously announced scheme. The government appears to put infinitely more energy into announcing its policies rather than actually implementing them,” said Munday.

Prof Donna Kinnair, the RCN’s acting chief executive, said: “With nursing student numbers falling and the number of unfilled nurse jobs projected to rise as high as 48,000 in the next five years, the situation is desperate.

“This is a small step in the right direction, but this kind of policy would benefit only a very limited group of people. If the government and NHS England want to attract more people to study nursing, and begin to tackle the increasingly dangerous shortfall in nurse numbers, we need more than tinkering.”

A spokesperson for NHS England said: “Supporting NHS staff and improving NHS mental health and learning disabilities are both priorities for the NHS and earlier this year we launched our largest ever campaign to recruit and train nurses in these specialist fields.”