Patients with a serious eye condition fear losing their sight if there is a no-deal Brexit because the government is refusing to say if an essential drug will still be available.

Ministers will not reveal which medicines are being stockpiled, leaving sufferers from glaucoma – who require daily drops of a medicine imported from the EU – facing huge worries.

The threat comes after similar fears were raised by diabetics who need insulin.

Theresa May has refused to “guarantee” the supply of all medicines if there is no deal – and health organisations have warned of “widespread shortages” unless plans are beefed up.

The situation has prompted an outcry from health experts and charities, who said patients should not be left with the distress of not knowing if their medicines will be available.

Chrissie Pepper, policy manager at the Royal National Institute of Blind People, said: “People with eye conditions deserve to be safe in the knowledge that they will be able to continue accessing the medication that will save their sight.

“During this period of uncertainty, the government should consider how it can reassure people and make sure they have the information they need.”

Niall Dickson, co-chairman of the Brexit Health Alliance, which brings together the NHS, industry and patients during the negotiations, said: “We need to avoid a position where patients are in any doubt that the drugs they need will be available.

“The government needs to provide that assurance and it needs to provide it soon, whatever the outcome of the negotiations.”

Two patients treated with Ganfort, the common treatment for glaucoma, told The Independent they feared going legally blind because their supplies come from Ireland and Spain.

A historic moment: thousands march to demand Final Say on Brexit Show all 65 1 /65 A historic moment: thousands march to demand Final Say on Brexit A historic moment: thousands march to demand Final Say on Brexit An estimated 700,000 people marched through London to demand a final say on the withdrawal agreement Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Red smoke from a canister hangs in the air as around 100,000 demonstrators march through London during a People's Vote anti-brexit demonstration savings banners and placards Anti-Brexit People's Vote March for the Future in London Rex A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Mayor of London Sadiq Khan takes part in the People's Vote March for the Future in London, a march and rally in support of a second EU referendum. 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Patrick Cosgrove (below), a retired former civil servant, submitted a freedom of information (FOI) request asking which drugs will be stockpiled but was told the government “does not hold information”.

The 69-year-old, living in Shropshire, said: “It’s a dereliction of duty to put us in a situation where a hard Brexit is possible and the supply of medicines could dry up.

“I don’t know if they know or not. If they do know what medicines are being stockpiled, why are they not telling me and reassuring me about this?”

Gill Sellen, a 63-year-old charity worker in Dorset, said: “Eye drops such as Ganfort have saved my sight so far, but the feeling of almost 25 years of care being ruined beyond 29 March 2019 is actually very real.

“If I do not use them, I will more than likely go blind. I might have 30 years ahead of me yet and it is a very hard thing to contemplate.”

The government conceded in July that medicine and food were being stockpiled, to guard against crashing out of the EU without an agreement, but controversy has raged ever since.

NHS providers, pharmaceutical companies and patient groups have joined forces to warn that ministers have failed to prepare adequately to ensure the flow of medicine.

“We do not believe that the current medicine supply plans will suffice, and we will have widespread shortages if we do not respond urgently,” their leaked letter said.

In the Commons, on 31 October, the prime minister refused to “guarantee the supply of medicines”, saying only that the government was “making contingency arrangements should no deal occur”.

In a TV interview, Matt Hancock, the health secretary, said “refrigerated capacity” was being built to ensure “unhindered flows of medicines to people in any scenario” – denying he was “panicking”.

But the government is refusing to release any information “about a company or a specific medicine into the public domain” and has forced drug companies and industry bodies to sign gagging clauses.

Mr Cosgrove said he put in his FOI to the cabinet office because the Ganfort he is prescribed for his hereditary glaucoma is imported from southern Ireland.

He was told to submit a second FOI to the Department for Exiting the European Union, which replied that it “does not hold information relevant to your request”.

The department warned that an identical request to the Department of Health and Social Care (DHSC) could be “subject to exemptions” and directed him to a “technical notice” on no-deal preparations, which says nothing about drug stockpiling.

Mr Cosgrove said he would be “stuffed” if his sight deteriorated to the point of legal blindness, adding: “I would have to give up driving, which means I would have to sell my house and move to a town.”

Asked by The Independent, the DHSC refused to say if Ganfort was being stockpiled, adding it was “preparing for a range of potential outcomes in the unlikely event of a no deal”.

“As part of our contingency planning we continue to work closely with pharmaceutical companies and storage providers to ensure the continued supply of all medicines that could be affected,” a spokesman said.

Nikki Joule, of Diabetes UK, said it was worried that only “some pharmaceutical companies” had said they were stockpiling insulin for a minimum of 12 weeks, as instructed.