Many of those killed were elderly people or those who were already weak or ill.

According to medical staff who treated patients at the time, few people realised the extent of the impact.

No one really noticed that more people were dying

Dr Robert Waller

Dr Robert Waller was working at St Bartholomew's Hospital in the capital in the early 1950s.

He says a shortage of coffins and high sales of flowers were the first indications that many people were being killed.

Death toll

"The interesting thing is that no one realised at the time that the no of deaths were increasing," he told the BBC.

People tried to protect themselves

"There weren't bodies lying around in the street and no one really noticed that more people were dying.

"One of the first indications was that undertakers were running out of coffins and florists were running out of flowers.

"The number of deaths per day during and just after that smog were three to four times the normal."

The smog, which lasted for five days, was so bad that it infiltrated hospital wards.

	:	Great Smog of 1952
Click here to see photos of the toxic fog

Maureen Scholes, a nurse at the Royal London Hospital at the time, recalls being unable to see from one end of the ward to the other because of the pollution.

"You couldn't see along the corridor that you walked in when you came on duty.

"You couldn't see actually from one end of the ward to the other and it's not that enormous a length."

Ms Scholes worked at the Royal London Hospital

Dr Waller adds: "In the wards, where there were many patients, you couldn't see clearly to the end of the ward."

Hospitals filled up quickly as many struggled to cope with the pollution.

"There were many patients admitted but there were too many affected and they apparently couldn't get into hospital and perished outside," says Dr Waller.

The smog prompted the government to introduce legislation to cut smoke emissions.

While the threat of smog has been tackled, other pollutants continue to pose a risk to people living in Britain's major cities.

Dr Tony Fletcher, of the London School of Hygiene and Tropical Medicine, says pollution is still responsible for causing respiratory problems in many people.

"We still have part pollution in the cities. The much finer particles are able to get deep into the lungs.

"There is a new problem of ozone which is more a problem in the summer than the winter but is also a cause of respiratory disease now."

Still a problem

Richard Mills, secretary general of the National Society for Clean Air, warns that there is still more to do to protect people from pollution.

"We are better off but not as much better off as we might have thought. Fifty years on the great smogs are gone but invisible pollutants are still taking a major toll on health.

"Some 20,000 in England alone suffer shortened lives each year."

He says vehicle emissions are the main culprits and believes the government should be doing more to tackle the problem.

He adds that the great London smog should act as a lesson to politicians now.

"All of us can learn from the aftermath of the great smog that you cannot just assume that because you cannot see the pollution that it is not there," he warns.