An investigation published by The BMJ has claimed that the NHS is impeding access to Gilead's high priced hepatitis C drugs Sovaldi and Harvoni.

In the investigation, researchers from the University of Cambridge, the University of Bath, and The BMJ, conclude that NHS England, unable to budget for broad access to these drugs, tried to alter the outcome of the NICE process, and when it failed, defied NICE's authority by rationing access to them.

"The investigation also exposes key weaknesses in our current system of assessing the value of new therapies and delivering them to patients – and asks, is company pricing to blame?" the authors said in a statement."

They add that during the course of the investigation, it has emerged how apparent panic over high prices and affordability led NHS England to deploy many delaying tactics, which succeeded in hampering timely access to these drugs.

Sovaldi and Harvoni, launched in 2014, have been highly controversial because, despite offering cure rates of over 90 percent, their prices range from around $90,000 per patient in the US to almost £35,000 in England. This has sparked a global debate about access to high priced medicines for governments with limited resources.

The report says that for Sovaldi, NHS England spuriously asked for six months to implement guidance (the mandatory 90 days and an additional three months), saying it needed time to set up a proper database to audit patients and usage of the new drugs. NHS England also tried to completely block Harvoni and two other competitor drugs undergoing appraisals at NICE, and questioned the level of clinical evidence.

NICE did eventually succeed in publishing guidance recommending these drugs for the majority of hepatitis C patients, but the authors note that NHS England is not fully following NICE's mandate, which requires that approved drugs are made available within the NHS. Instead it has restricted use of the new drugs by forcing quotas on clinical teams around the country.

They continue: "This rationing has left many clinicians facing hard decisions and difficult conversations with patients who have already seen their treatments delayed several times. And there is now growing evidence that some frustrated patients are turning to overseas 'buyers' clubs' to source the drugs at their own expense."

NHS England says its delivery of drugs is entirely within the parameters of the NICE guidance - and highlighted Gilead's pricing as the key reason why treatment was being delayed. This echoes major criticisms of Gilead's pricing strategy in the US, where legislators said the company had adopted a strategy "designed to maximise revenue with little concern for access or affordability".

A spokesperson for NHS England said it was "exploring the potential for a longer term strategic procurement for a supply agreement with the industry to improve the affordability of and access to treatment further".

The Hepatitis C Trust, a patient advocacy organisation, believes the NHS is risking legal action over its decision to ration them. Chief executive Charles Gore said the Trust has "already spoken to solicitors to take on any cases that come up, because we are not going to have NHS England pick on a disenfranchised group".

Andrew Ustianowski, a consultant in infectious diseases at Pennine Acute Hospitals NHS Trust, added: "I think some people in NHS England would love to clip NICE's wings and turn it into a kind of recommendatory rather than mandatory body. And if you are going to choose a fight then choosing this battlefield is quite a sensible thing to do – a marginalised population, very high-cost drugs."

Dr Ustianowski resigned from NHS England's clinical advisory group, in protest at deliberate attempts to delay access to treatment. "I didn't want to be associated with what was happening," he told The BMJ.