Higher numbers of complaints about breathing difficulties are thought to have been brought on by record pollution levels in recent days.
Air pollution in the east of England reached the top of the scale as a 'perfect storm' of conditions blanketed parts of the country.
Our region is one of the worst-affected by "very high" levels of air pollution today, with much of the East stuck under a cloud of smog.
The south east, east Midlands,Yorkshire and Humberside, north west and Merseyside and the north east are still suffering from "high" air pollution levels, Defra has warned.
A fresh air mass arriving later today is expected to push the pollution eastwards over the North Sea.
The number of people experiencing breathing problems increased by 34 per cent on Thursday, London Ambulance Service has said.
The capital experienced "very high" pollution levels yesterday but air quality is expected to improve today.
We saw a 34% increase in patients with breathing problems yesterday compared to an average Thu
People with asthma may also find that they need to use their inhaler more frequently, have it with you at all times
Daybreak's Chief Correspondent Richard Gaisford tweeted from London's Parliament Hill:
Environmental campaigners have urged politicians not to ignore the cloud of smog that has smothered parts of the UK over the last few days, saying they are "playing with people's lives".
Friends of the Earth's Jane Thomas told Daybreak, "29,000 people a year die prematurely in London alone" from pollution created by emissions.
Air pollution levels remain high across parts of England and Wales but are expected to reduce later today.
The Department for Environment, Food and Rural Affairs (Defra) reports that more than 20 areas from northern England down to the South East are still gripped by high levels of pollution this morning.
But a fresh air mass arriving later is expected to push the pollution eastwards over the North Sea, weather forecasters have said.
Pollution levels remain 'high' across England and south Wales and 'very high' in London, the Department for Environment, Food and Rural Affairs (Defra) has said.
Showery outbreaks of rain will persist overnight across northern England and much of Scotland.
Misty and murky conditions will be forming out toward the North Sea coast, and we are still pulling up that polluted air from the south-east.
Things will be changing overnight, however - a south-westerly air flow will feed in much cleaner, fresher air.
The number of 999 calls from north-west patients struggling with breathing problems has soared by 15% this week, the region's ambulance has said.
According to the Manchester Evening News, the North West Ambulance Service has seen 985 such calls between Sunday and Wednesday compared to 858 between in the previous four days.
A spokeswoman for the service told the newspaper that while the increase appeared to be linked to an increase in pollution levels, the cause was not completely certain.
West Midlands Ambulance Service has experienced a noticeable spike in call-outs linked to breathing problems and chest pains.
Daily figures for calls reporting breathing or chest problems were largely level at around 460 on Friday, Saturday and Sunday last week.
But the corresponding figures for the first three days of this week were 547, 510 and 501.
The service covers Shropshire, Staffordshire, Warwickshire, Herefordshire and Worcestershire.