A band of healthcare professionals and charities has warned political leaders that health and social care services are at “breaking point” following “an era of unprecedented austerity”.

In a letter to Prime Minister David Cameron, Labour leader Ed Miliband and Deputy Prime Minister Nick Clegg, published by The Independent, signatories* including the British Medical Association and several of the Royal Colleges write that the NHS has been through “the longest, and most damaging budget squeeze in its history,” and warn that the situation “cannot go on”.

“Signs of a system buckling under the twin crises of rising demand and flatlining budgets are everywhere,” they claim, highlighting a shortage of GPs, over-stretched maternity services, A&E departments missing waiting times, delayed cancer referrals, and a lack of mental health beds, as well as crippling costs of social care and failing dementia services.

Last week Cameron said he would protect the National Health Service budget in real-terms from 2015, while Miliband promised £2.5 billion a year more and Clegg £1 billion extra in 2016/17 to help address cash issues. But critics fear these pledges will barely scratch the surface of the £30 billion funding gap expected by 2020.

And while welcoming the fact that the NHS “has risen to the top of the political agenda, and some new spending commitments have been made,” the signatories have called for “a comprehensive, fully costed, long-term spending plan if an NHS true to its founding principles of universal healthcare, provided according to need not ability to pay, is secured for future generations”.

They also want a guarantee that the NHS will be protected from another top-down reorganisation “which is not in the best interests of patients, and distracts from the severe, long-term funding pressures facing the health service”.

*Mark Porter, chair of council, British Medical Association

Peter Carter, chief executive and general secretary, Royal College of Nursing

Jane Dacre, president, Royal College of Physicians

Maureen Baker, chair, Royal College of General Practitioners

Cathy Warwick, chief executive, Royal College of Midwives

Hilary Cass, president,  Royal College of Paediatrics and Child Health

David Richmond, president, Royal College of Obstetricians and Gynaecologists

Caroline MacEwen, president, Royal College of  Ophthalmologists

Jeremy Hughes, chief executive, Alzheimer’s Society

Henny Braund, chief executive, Anthony Nolan

Michelle Mitchell, chief executive, the MS Society

Lesley Anne Alexander, chief executive, Royal National Institute of Blind People

Siobhan Dunn, chief executive of Teenage Cancer Trust

Peter Swinyard, GP Swindon and national chairman, The Family Doctor Association

Moira Auchterlonie, chief executive, Family Doctor Association

John Middleton, acting president, Faculty of Public Health