The case of Ming Zhu illustrates the problem with the coronavirus antigen test – which ascertains if somebody currently has the disease. Zhu is a doctor at St George's Hospital in London. He came down with coronavirus symptoms last week and is self-isolating at home. But when he was swabbed for the disease, to his surprise, the test came back negative.

"The test itself only has a 60-70 per cent sensitivity – which is a term we use to describe the ability of a test to come back as positive when the presence of the disease is truly there," says Zhu, pointing to an Oxford study that assessed the effectiveness of the oral and nasal swabs that are used for antigen tests.

"If it comes back positive you obviously have it," says Zhu. "But if it comes back negative and you have all the symptoms, it should still be treated as positive anyway. Due to the low sensitivity of the test, countries like Italy insist on swabbing people three times."

Therefore Zhu, despite testing negative for coronavirus, will continue to self-isolate at home. The Oxford study that he cites cautions that its findings are only based on preliminary data, but clearly many NHS trusts are taking it very seriously.

"I don't entirely trust the test, but at the moment it's the best thing we've got," says Ishani Rao, a doctor at another trust on the outskirts of London, who says increasingly doctors are looking for symptoms not prescribed by the government such as painful eyes and stomach upset.

"Apparently the swabs that we're doing – which are throat and nose – they're only about 65 per cent specific. Obviously we're seeing about 100 patients a day. So even if doctors are coming back with negative tests but are still symptomatic for anything we could transmit – people are still staying at home."

Squeezing in a spare moment after busy night shifts, three doctors spoke to me about their work in and around London. All three suggested they were facing shortages of kit.

"The majority of the time right now, unless we are doing aerosol generative procedures, we just wear the plain surgical masks with a plastic apron – the disposable ones – along with gloves," said Zhu, who knows of six colleagues who have also come down with coronavirus. Patients generate aerosol by coughing or sneezing. "The surgical mask is awful. It has a lot of different leaks. It's not by definition a fitted type of protective gear."

"Generally most patients are being seen with an apron and a normal surgical mask – which is probably not ideal," agrees Anant Shah, who works in another trust on the outskirts of London. "If any patient is generating aerosol, then there seems to be enough FFP3 masks for those patients to be seen. In an ideal world we would all have FFP3 masks."

FFP3 masks are the fitted mouthpieces that form part of the full personal protective gear (PPE) outfit. In her trust, Rao has also had access to masks for patients who are coughing and sneezing. But, pre-empting shortages, staff have begun rationing kit and taking matters into their own hands.

"My colleagues are probably spending £70-90 on personal protective gear online," says Rao. "At the moment we are relying on charity donations, dentists are giving us all their gear, medical fetish sites are giving us their disposable scrubs."

While morale is strong, all three doctors said intensive care units were running close to or exceeding capacity in their respective hospitals.

"I trained in London so I have a lot of friends who are still working in central London. They were full up about two weeks ago," says Rao. "We're now also at full capacity; 80 per cent of those beds are [filled with] suspected or confirmed coronavirus patients. We're having to prioritise patients that we think will have 'the best clinical outcomes' which is a really difficult decision to make."

In plain English, "best clinical outcomes" means staff are having to make terrible choices about ventilators and beds, about who is more likely to live if they are teated. Rao estimates she is referring ten to 15 patients a day to the already full intensive care units.

"It's a juggling game trying to work out who is going to have the best clinical outcomes with the short resources that we have."