More than 30 charities ( Including the NKF) have written to the three party leaders urging them to commit to reversing NHS measures to increase rationing of medicines.
Health officials last month brought in new thresholds which mean access to one in five treatments could be delayed or restricted.
Under the rules, all drugs expected to cost the NHS a total more than £20 million a year will be checked against new “affordability criteria”.
The cost threshold set by NHS England could affect medicines costing as little eight pence a day, if used commonly enough, as well as high cost medicines used for rare diseases.
Rationing body the National Institute for Health and Care Excellence (Nice) has said it is likely to affect around 20 per cent of drugs it assesses, with the process including changes that the head of its rationing body has previously described as “unfair”.
In an open letter to Theresa May, Jeremy Corbyn and Tim Farron, the charities - which include Parkinson’s UK, the Children’s Heart Federation and the MS Society - ask all the parties to commit to reversing the changes.
The signatories – all members of the Specialised Healthcare Alliance – said that the measures “stand to restrict and ration treatments for people with rare and complex conditions, and were implemented without the agreement of Parliament.”
The letter comes as political parties prepare to publish their manifestos for the election.
Caroline Harding, chief executive of Genetic Disorders UK said: “Under these plans, some of the most critically ill patients are being denied access to potentially life-changing treatments.
“Any decision to ration access to medicines should be taken by ministers, not unelected officials.”
Kay Boycott, chief executive, Asthma UK, said:
“There is a real risk that these plans will turn the clock back on access to life transforming treatment.”
Sarah Vibert, chief executive, Neurological Alliance, said: “Politicians from all sides should pledge to rethink these damaging proposals.
“It is completely unacceptable that patients with neurological conditions risk being denied access to treatment solely on the basis of cost.
None of the parties have formally published their manifestos. But the draft Labour manifesto, leaked last week, said: “Labour will tackle the growing problem of rationing of services and medicines across England, taking action to address postcode lotteries and making sure that the quality of care you receive does not depend on which part of the country you live in. We will ensure that NHS patients get fast access to the most effective new drugs and treatments."
Jonathan Ashworth, shadow Health Secretary, said: “There is a real and growing worry that Theresa May’s ongoing underfunding of the NHS means patients just aren’t getting access to new medicines. Patients need fast access to medicines and treatments which are recommended by Nice as being clinically and cost effective. Labour is committed removing the barriers which are being put in place and to ensuring that NHS patients get fast access to the most effective new drugs and treatments.”
A Conservative spokesman said: "NHS spending on medicines and treatments is now second only to staffing costs - in fact, the NHS in England spent more than £15 billion on medicines last year, a rise of nearly 20 per cent since Labour left office. But we can only ensure more patients than ever get outstanding care if we continue to invest in the NHS on the back of a strong economy - something Jeremy Corbyn and the other parties who'd prop him up in Downing Street simply could not do."
Liberal Democrat Health Spokesperson Norman Lamb said: “This is a shameful retreat from the core principle of the NHS, that treatment should be available to patients regardless of their ability to pay.
“The rationing of treatments is an inevitable consequences of this government’s chronic underfunding of the NHS. NHS England is caught between a rock and a hard place because they simply don’t have enough resources.