A stinking cloud of gas has been hanging over large areas of England after a leak at a French chemical plant, sparking thousands of calls to emergency services.
The sulphurous stench - likened to rotten eggs - is said by officials to be completely harmless.
But police in Kent, Sussex and Surrey began to receive floods of calls from concerned residents on Tuesday morning - and by afternoon there were reports of the unwelcome whiff in Oxfordshire and as far north as Northampton.
The gas, called mercaptan, was accidentally leaked from a factory in the northern city of Rouen and before long had drifted over the English channel.
It is sometimes added to natural gas to alert people to gas leaks
The National Grid, which would normally deal with up to 10,000 calls countrywide in a day, had received an "unprecedented" 100,000 calls by 2pm.
Sussex Police said: "The smell is from an additive to the gas which has an unpleasant aroma but is not toxic and there is no danger to the public."
The Health Protection Agency (HPA) said the gas had diluted since entering the air over England, and, although it may cause some people to feel slightly sick, it will dispel naturally.
The French interior ministry confirmed that a gas factory owned by the company Lubrizol, a subsidiary of investor Warren Buffet's Berkshire Hathaway group, was to blame.
The firm's operations director, Pierre-Jean Payrouse, told French radio that they were trying to contain the leak but the cause was unknown.
In Rouen, more than 10,000 people have phoned the emergency services to complain about the smell.
The Metropolitan Police tweeted: "We are aware of reports of a strong noxious gas-like smell in some south-east London boroughs - no risks to public."