If we thought our health service was prepared for the coronavirus, the past few days have brought a shattering reality.

Here, in a chilling dispatch from the front line, one doctor recounts the moment Covid-19 struck and overwhelmed a major London hospital – and how doctors and nurses watched helplessly as patients died an excruciating death...

Have you ever seen someone gasping for their last breaths? Not many have, but for those who have experienced it, you never forget the horror. I wish I could forget all the faces of the dying I saw last week.

The look of panic across every face, the chugging sound people make as they desperately try, and fail, to get oxygen in their lungs. It doesn't leave you.

I have been a doctor for more than a decade. In that time, I thought I had seen everything there was to see. But nothing could have prepared me for the terror that coronavirus would unleash.

It was just after lunchtime on Saturday when the nightmare began. The siren sounded on my pager to tell me a patient had had a respiratory arrest and I rushed across the hospital to attend a man in his 70s with Covid-19 whose heart had stopped beating.

What I was met with when I arrived was sheer panic. The staff, through no fault of their own, were hesitant in exactly how we should respond.

It was an early indication of how grossly under-prepared as a country we are for treating this virus. The compressions to resuscitate him proved futile.

Along with two nurses, a senior doctor and an anaesthetist, who was managing his airway, we were powerless as Covid-19 cruelly claimed a victim right before us.

He was gasping for breath with every ounce of life that he could muster. I could see the terror in his eyes. He knew.

This was compounded by the terror in the faces of the staff present. They are all brilliant colleagues, respected professionals who have, like me, been doing their jobs for a long time. There shouldn't have been any fear for them. But there was. I could see it. And I felt overcome with it, too.

I am a senior medical doctor covering all wards including high dependency at a busy hospital in London. We're used to being stretched and working long shifts without breaks to deal with any number of emergencies that come through the door every day. But last Saturday was different.

Yes, we knew that the virus was coming but we weren't prepared for this. A few hours before the first Covid-19 death at the hospital, we were suddenly forced to restructure our wards to accommodate the vast numbers of sufferers who were being admitted in critical conditions.

I am a doctor. I am trained to block out the inner voice of panic that comes to all of us in times of extreme stress. But there was no blocking out this time. There it was, bellowing at me continuously: 'Oh my God, what is happening?'

We knew this man was just the first one we would see die in this excruciating manner. The child in me was thinking: 'If only I can save him, perhaps all those people piling up in our wards will be OK, too.' But this, of course, is real life. Not a children's story.

As he cruelly slipped away, my heart sank. There was no time to dwell, though. For we soon had a full ward of sufferers. What's more, despite restructuring the wards to ensure there was room for the coronavirus sufferers and that they would be totally isolated, it soon became apparent that the virus was already rampaging throughout the hospital.

Not long after his death, my pager went off to attend someone on a regular ward who had taken a turn. Lying in an open bay, they were burning up with a serious fever. I could cry thinking about it.

This individual had been admitted to hospital for something totally unrelated and now, here, lying before me, it was clear they had caught the virus in the very place they had every reason to expect would help them get better.

My eyes darted around the ward. He was surrounded by other beds full of patients, as well as nurses and doctors who were not protected – myself included.

At this point I had been working for nine hours straight on an empty stomach, having only taken one toilet break. There would be no let-up. For he was merely the first discovery.

Almost simultaneously sufferers began popping up, as my pager's siren went into overdrive. I rushed between wards, attending to alerts coming from all over the hospital.

With each new discovery, all I could hear was my inner voice screaming louder with each new discovery: 'No, no, no, no. Please God, no.'

For some of the population, I realise that this must be hard to comprehend. According to one graphic I have seen shared on social media, Covid19 is little worse than the winter flu. But let me tell you, it is so very much worse.

Besides the far more aggressive lung disease it has the ability to cause, its ability to spread totally differentiates it from any flu.

Many of you reading this might have assumed that the virus is only serious for those with 'underlying health issues'. It is a clever term, for it works to distance many of us from it. Yet I have seen first-hand how quickly it spreads.

I lost count of the number of times I have found sufferers in different wards. Any hope we'd had of keeping Covid-19 sufferers separate from the rest of our patients became almost totally blurred as the influx just became greater, and greater, and greater. You instinctively know it is the coronavirus. There is no mistaking it.

Patients who come in for totally different reasons do not just suddenly develop high fevers. When we think it's likely that someone is suffering from the virus on a non-isolated ward, we take them to a side room and swab them.

It takes two days to get the results, which provides another logistical challenge.

While we wait for test results the patient can't return to a normal ward in case they have the virus, but they can't be moved in with Covid-19 sufferers in case they don't.

Me? I am asymptomatic, but I have been exposed to it – frequently. I am, therefore, most likely carrying it, as are most medics up and down the country.

Absurdly, I have not been afforded a test – and the NHS's approach for staff is that until you have symptoms you don't self-isolate. Why? Because we simply do not have enough staff for them to be disappearing before symptoms appear, regardless of whether they are likely carrying it or not.

As a doctor you should be saving lives. But for the first time in my career I have to face the fear that as a doctor I could be a silent killer. I have no choice but to block out that fear and just get on with it.

Towards the end of last week, it became apparent that there is very little we can do to halt the spread of this aggressive and unrelenting virus. Many patients simply do not respond to treatment and oxygen masks and we are left with no choice but to make them 'comfortable'.

Even with morphine and the sedative midazolam to help numb pain and ease breathing, the deaths have been excruciating. That is why I wish that I could forget last week, pretend it is some nightmare. But it isn't. It is now our new reality.

The virus has forced doctors to do something we should never have to do: play God.

Within the space of a few hours last Saturday, what I had known my job to be changed irrevocably. For we must now make ethical decisions on who to save and who to let die on a scale that no doctor alive today has ever faced.

I would love to say that those ethical decisions are made with time, patience, and care. But last week? It was as quick as can be. No doctor should be forced to choose between patients. But we now have no other choice.

It is never an easy task to tell someone's loved one their mother, father, wife or husband is not a candidate to go to intensive care because they have serious underlying health issues and, because of their old age, there is nothing we can do.

Italy has already stopped intubating patients over 60. Whenever you call a patient's family to let them know that their loved one is dying, the first response is usually 'How long?' followed by asking if they can see them.

Once a patient is in a critical condition with this virus, there is never more than a couple of hours before it kills. So far, we have been allowing individual visitors dressed in protective gear to say their final goodbyes, but for how much longer will this be the case if the death toll soars and protective equipment becomes in short supply?

Several times this week, families have unfortunately not accepted their loved ones' fate and pleaded with us to keep trying to fight the virus off. Those conversations stay with you.

There are now close to 150 known sufferers in the hospital but I suspect it could be many times more than that. We are at breaking point, with virtually no space to treat those suffering. And this is barely the tip of the iceberg.

Little over a week on from that horrendous Saturday we are already on the cusp of declaring a critical incident, which means we physically have too many critical care patients and no room to take any more.

There is at least one other hospital where this has already happened. As medics, we are all petrified of what we face in the coming weeks and months. Are we prepared? No. We do not even have enough protective clothing.

These fears are compounded by the dangerous under-dressing of our staff because of shortages. And as for personal protective equipment, for some unknown reason Public Health England has said that it is fine for us to be wearing a surgical mask with air gaps rather than a full-protection mask with an air-filter system, a plastic apron and a pair of gloves.

That might sound like enough, but, in reality, we are reduced to flimsy, long-sleeve aprons (some doctors at other hospitals have even complained about wearing sleeveless aprons), and a mask with – effectively – holes in it.

Many saw the frightening scenes coming out of Italy's grossly overcrowded hospitals at the end of last week.

The brutal truth is that we are facing exactly the same immediate future here. The virus is wanton in its destruction.

Make no mistake, we are at breaking point and we are little more than a week in.

It feels like we are trying to play some sort of computer game and with each day we enter a new, harder level. We simply cannot keep up. How much worse will it get?

Truthfully, I shudder to think.