Almost 3,000 people with cystic fibrosis will miss out on a "breakthrough" treatment after the health watchdog turned it down for use on the NHS.
The National Institute for Health and Care Excellence (Nice) 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 over a two-year period, potentially adding years to life.
Only around half of people with cystic fibrosis live to celebrate their 40th birthday.
The drug, which is approved in the US, Germany and France, is for people with the F508del mutation, which causes the production of an abnormal protein that disrupts how water and chloride are transported in the body.
Having two copies of this mutation (one inherited from each parent) is the leading cause of cystic fibrosis.
Ed Owen, chief executive of the Cystic Fibrosis Trust, said: "We are very disappointed by this decision.
"It demonstrates the weakness of the current system, and Nice has been unable to confidently predict the long-term benefits of the drug.
"However, new data published last month shows the positive impact of Orkambi over a two-year period to slow the decline in lung health. Our Cystic Fibrosis Registry offers additional means to collect real-world evidence while ensuring people with cystic fibrosis have access to the first therapy that tackles the underlying cause of the condition for almost 3,000 people."
Simon Bedson, senior vice president at Vertex, which makes the drug, said it was now in talks with the Department of Health to agree a price that might make the drug accessible.
The Cystic Fibrosis trust wants to use its registry to see how the drug performs in a real-world setting.
Mr Bedson said: "As we've said for many months, the single technology appraisal process (used by Nice) is not appropriate for assessing medicines, such as Orkambi, for rare diseases like cystic fibrosis.
"Vertex has submitted an access scheme to the Department of Health, and we urge the NHS and the Government to consider this proposal."
Orkambi costs £104,000 per patient for every year of treatment.
Professor Carole Longson, director of the Nice centre for health technology evaluation, said: "We know how important a new treatment option would be for people with cystic fibrosis; but for the benefits it offers, the cost of Orkambi is too high.
"We can only recommend treatments when we are certain they are both clinically effective and represent good value for money.
"If the company is able to put forward a proposal that provides Orkambi at a cost-effective price, we would welcome it."