Cystic fibrosis patients are to stage protests over the lack of availability of a treatment which has been hailed as a "major step forward" for people with the condition.
Last year the National Institute for Health and Care Excellence (Nice), which helps decide which new treatments should be available on the NHS in England and Wales, rejected the drug Orkambi, which has been shown in clinical trials to improve lung function and respiratory symptoms in people with the genetic condition.
The charity the Cystic Fibrosis Trust said that since Nice undertook its appraisal, new data had been published that suggested Orkambi almost halved the rate of decline in lung function in people with the disease.
It said that studies have shown that if children with cystic fibrosis start taking Orkambi early enough they could have a near-normal life expectancy.
Cystic fibrosis is a life-shortening genetic condition that causes fatal lung damage. Only around half of people with cystic fibrosis live to celebrate their 40th birthday.
The CF Trust said that the drug has been licensed in the UK for more than two years but it is still not available on the NHS as governments across the UK and Orkambi's manufacturer, Vertex, have not been able to agree on a price.
Protests are to be staged outside Downing Street, the Scottish Parliament and the Welsh and Northern Ireland Assemblies against the lack of availability of the medication.
The CF Trust said that of the 10,800 people in the UK with cystic fibrosis, 3,296 could benefit from the drug.
James Barrow, head of external affairs at the Cystic Fibrosis Trust, said: "Cystic fibrosis is a cruel and life-shortening condition that places a huge daily burden on people living with the disease.
"Orkambi is a major step forward in the treatment of cystic fibrosis, which could help people live longer and has the potential to save the lives of thousands in the UK.
"The drug deals with the underlying cause of cystic fibrosis and prevents irreversible lung damage, which is especially important for children as they stand to benefit from it the most.
"If a deal between the Government and the manufacturer over the price of Orkambi is not reached soon, we fear people in desperate need of the drug will run out of time."
Liam McHugh, from Castlederg in Northern Ireland, whose daughter has cystic fibrosis, is planning to attend one of the demonstrations.
He said: "My daughter is one of the few people in the UK lucky enough to get Orkambi as part of a clinical trial. For Rachel it has been nothing short of a wonder drug.
"When Rachel was born we were told she wouldn't make it to adulthood. She is now 25 and, because of Orkambi, her lungs are better than ever. Looking at the strong and determined medical student she has become today, I'm the proudest father on the planet.
"I wish everyone dealing with this devastating disease could have the same chance of life as my daughter has been given, which is why I'm protesting to make Orkambi available to everyone that needs it."