"We coped, but only just," Baroness Heather Hallett concluded in the inquiry's third report, released on Thursday.
She said UK healthcare systems "teetered on the brink of total collapse".
Module 3, the third of the inquiry's 10 investigations, has examined the impact of COVID on healthcare systems across the four nations.
It investigated how governments and society responded to the pandemic, the capacity of healthcare systems to adapt and the impact on patients, their loved ones and healthcare workers.
The report, based on the testimony of 97 witnesses, found the UK entered the pandemic "ill-prepared", with this fragility leading to "profound consequences" once the crisis hit.
It says that, despite the best efforts of healthcare workers, many COVID patients did not receive the care they would otherwise receive, and non-COVID patients had their diagnoses and treatment delayed.
Baroness Hallett said healthcare workers "carried the burden of caring for the sick in unprecedented numbers" during the pandemic.
"It came at a huge cost to them, their families, their patients and the loved ones of patients," she added.
The system's collapse was only "narrowly avoided thanks to the extraordinary efforts" of healthcare workers, she said.
Baroness Hallett said: "The enormous strain placed upon the healthcare systems was unprecedented.
"Those working within it were obliged to work under intolerable pressure for months on end."
The report makes 10 recommendations "to prevent healthcare systems being overwhelmed in the next pandemic".
These include increasing capacity in urgent and emergency care and ensuring hospitals have "surge" capacity, strengthening the body responsible for infection prevention and control guidance, and better advance care planning.
Campaign group COVID-19 Bereaved Families For Justice labelled the report and its conclusions as "utterly damning".
It said the "devastating" impact on UK healthcare systems during the pandemic could have been avoided.
"Years of austerity left the NHS dangerously exposed, without the staff, beds or resilience needed to withstand a major shock," the group said.
"That was a political choice.
"And when the pandemic hit, those in power failed us again.
"They failed to act early enough, failed to follow the evidence, and failed to respond with the urgency the moment demanded."
Looking ahead, the group says the UK's health service is now in a worse position to cope with another pandemic than it was six years ago.
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It says the current meningitis outbreak in Kent "underlines why restoring resilience and capacity to our health system should be a matter of priority for those in power".
"That's why what happens now is so important. This report must not be left to gather dust and its recommendations should be the floor, not the ceiling, of the government's ambitions.
"We urge the government to use this report as a catalyst for change. Failing to do so would be unforgivable."
A government spokesperson said "it is committed to learning the lessons of the COVID Inquiry".
They added: "We will consider Baroness Hallett's findings and recommendations carefully and respond in full in due course."
Eden Bunn was among five people in a blue VW Polo, which veered off the road into the River Nene near Wisbech at about 8.20pm on Tuesday. Her body was recovered by divers on Wednesday.
Searches are continuing for 18-year-old Declan Berry, from Wisbech, who is believed to have been driving the car. His family and friends said they were "absolutely devastated beyond words".
Police said three other people in the vehicle managed to get out and were taken to Queen Elizabeth Hospital in King's Lynn with non-life threatening injuries.
Among the three, a 16-year-old girl and a man aged 18 have since been discharged, while another 16-year-old girl remained in hospital on Thursday.
Ms Bunn, from Sutton Bridge, Lincolnshire, was believed to be a rear-seat passenger when the collision happened.
In a tribute, her parents, Lisa and Dean, her brother Jay, sister Shelby and nephew Axl said: "Eden was the kindest, most loving girl we could ever wish for.
"Her horses - Daisy and Dolly - were her world, and she was ours.
"Words cannot describe the tragedy that will stay with us until we are able to meet her again."
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The vehicle was travelling south on North Brink in Wisbech St Mary's when it left the road.
At least a dozen emergency services personnel and a white forensic tent could be seen on the riverbank on Wednesday.
Detective Inspector Craig Wheeler, from Cambridgeshire Police, said the search for Mr Berry "could be a timely process" due to the "challenging nature of the river".
Mr Wheeler said: "This is a truly devastating collision, for all involved.
"My thoughts are with the friends and family of Eden and Declan during this truly horrific time.
"Our investigation is at an early stage but I would appeal to anyone who may have seen the collision or the blue VW Polo in the Wisbech area between 7pm and 8.20pm on Tuesday to contact police."
However, allow me to make the case that this document published by the government today represents something very important for all of us. And the reason, surprising as this might sound, has nothing to do with steel.
The strategy itself is, for those of us interested in such things, a big moment for the steel sector. There will be more money given out to steel producers - about £2.5bn - some of it going to the British Steel works in Scunthorpe that have been effectively nationalised, some going to support private steel makers around the UK in their efforts to produce lower carbon metal.
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Perhaps the most interesting of all the ambitions contained within it is a pledge to try to raise the proportion of steel we use in this country that is also made in this country. Right now that proportion is running at a record low of 30%, which, when you think about it, is rather depressing.
Think of all those wind turbines dotting the countryside and offshore, or for that matter much of the infrastructure surrounding us. Most of that still is not made - indeed cannot be made - in the steelworks and with the steel equipment we have in this country.
The ambition of the strategy is to raise the proportion of domestically produced steel to 50%, which is certainly better than the current level but is basically back to the level that used to prevail before COVID.
However, a far more significant element of the Steel Strategy - the bit that matters to all of us - concerns trade rules.
The background here is important. For some years British steel producers have struggled to compete with their overseas counterparts. Take something like galvanised steel: right now the country is facing an influx of very cheap galvanised steel from countries like Vietnam and Turkey. Most of those producers enjoy subsidies and tax breaks their British competitors do not.
The upshot is it is fiendishly difficult, if not impossible, for British producers to compete. This is fast becoming an existential crisis for the industry. There have been some trade barriers on this kind of steel, but they were due to expire this June, and anyway, were not particularly prohibitive. In fact, anyone who wanted to import cheap galvanised steel from Turkey or Vietnam was able to do so without paying any tariff whatsoever.
The centrepiece of the steel strategy is a brand new tariff of 50% on many of these steel imports and (just as, if not more important) new, lower quotas on those steel imports.
Now, in some senses this is not particularly surprising. At some point the regime needed to be updated - it was due to expire soon, after all. And Europe already has tariffs coming in that look very similar to these new British ones.
However, there is something more significant about this moment. It is the first time since the beginning of the most recent trade war - indeed the first time since Britain took back control of its trade policy post-Brexit - that it has raised tariffs to these kinds of levels.
It's very hard to make like-for-like comparisons given the convoluted detail of trade barriers, but the long and short of it is that these are probably the biggest increases in trade barriers imposed by a British government in at least a generation.
While other countries, most glaringly America under President Donald Trump, had raised many of their tariff barriers, up until this moment Britain had held firm. For many ministers this was a matter of national pride. This after all, after all, is the country that "invented" free trade, the country that abolished the Corn Laws in the 19th century and brought the worlds the notion of "comparative advantage". Many felt that to raise tariffs, even in an environment where everyone else was, would be an abomination.
However, it is a sign of the times but now that is precisely what this government has done. Britain will now have some of the highest steel tariffs it has imposed in its entire history, in an effort to protect its domestic industry.
Britain, in short, is dipping its toes into the waters of protectionism.
Many, including the government itself, will point out that the way these new tariffs are structured is far more sophisticated and far less brutal than the tariffs imposed in America. They will point out that they are mostly just mirroring what's happening in Europe.
Even so, it's hard not to conclude that this represents a watershed moment. This new Steel Strategy may look, on the face of it, like a boring, arcane document for a relatively small sector of the economy. But, an economic and historical terms, it is dynamite.
Crews from other areas were called in as one of the engines from Old Kent Road was at another incident at the time.
Four fire engines and around 25 personnel tackled the blaze on the first floor of a six-storey building in Cooper's Road, Southwark, on Wednesday.
One teenage boy made it out before firefighters arrived and was taken to hospital, while another died at the scene, London Fire Brigade (LFB) said.
The first emergency call was received shortly before 3pm.
Crews from Dockhead, Dowgate, Shadwell and Whitechapel went to the scene and the blaze was under control just after 4.30pm.
A 64m turntable ladder appliance from Old Kent Road fire station was on the scene within six minutes of the call, an LFB spokesperson said.
The spokesperson added: "Another appliance from Old Kent Road was out at a different incident but did return to the scene of the incident later."
The cause is being investigated by the LFB and Metropolitan Police.
Police Scotland said it was alerted to a report of a crash involving a pedestrian on the M80 at Denny at about 12.20am on Thursday.
Emergency crews attended, and the 44-year-old man was pronounced dead at the scene.
No other injuries were reported.
The motorway was closed in both directions between J9 and J8 at Sclandersburn Road overbridge.
The northbound lane reopened shortly after 3.30pm, with the southbound lane given the all-clear at about 4pm.
Sergeant Michael Shillington said: "Our thoughts remain with the family and friends of the man who died at this difficult time.
"Our enquiries are ongoing to establish the full circumstances and I would ask anyone who witnessed the crash and hasn't yet spoken to officers to get in touch.
"I would also appeal to anyone who was travelling in the area around that time and who may have dashcam footage which could assist to contact us."
During rush hour, motorists were warned that the traffic tailbacks were running at about an hour on the northbound road and 20 minutes on the southbound lane.
Drivers in both directions were faced with diversions of approximately 17 miles.
In response to a question on X about the length of time the road had remained closed, Traffic Scotland said: "Due to the serious nature of the incident unfortunately there are no timescales with police investigations ongoing."
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Announcing the reopening of both lanes, Traffic Scotland added: "Traffic beginning to revert back to normal levels for the time of day."
The Scottish Fire and Rescue Service (SFRS) told Sky News it was not called out to the crash.