First order problem, the hospitals have no beds. This means that ambulances end up waiting for hours and medics twiddling their thumbs at the ER until the staff can finally take the patient. Medics can't just abandon the patient because there legally needs to be a proper handoff. So your emergency can't be responded to quickly because we can't trivially spin up thousands of new medic units to spend all their time waiting in line at the hospital.
Second order problem, the hospitals have no beds because of a lack of long term care services. From the article...
> There is an acute lack of beds in the accident and emergency department, or A&E, as emergency rooms are called in Britain, which are overcrowded because of an inability to find room for patients elsewhere in hospitals. That is because patients ready to be discharged from the hospital often have nowhere to go as a result of dwindling social services — which have been hobbled by a lack of government funding and severe staffing shortages.
Now the question is why aren't there enough non hospital care services? Could be many reasons, but I'd speculate that it's a combination of a) an increasing population of old, sick people who need care in a society whose demographics are beginning to turn upside down, and b) because Brexit means it's drastically harder to import poor, foreign workers willing to do the shitty job of elder care for low wages. If this prognosis is correct, it starts to beg the question of whether Britain's world renowned health care system was only possible because it could extract excess, cheap labor from poor countries to take care of their old people, when Britain's own young people were never going to do that work for the wages offered.