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The gassy smell affecting the south east is from what is called a 'stenching agent' Health officials say it is not harmless
It happened on Monday at the plant in Rouen, about 75miles west of Paris, and was first wafted south by the winds, before being blown across the Channel to us.
The police, fire service and gas companies say they have received dozens of calls from worried Sussex and Surrey residents about the smell this morning.
You have also been tweeting and emailing us to say where it has reached. The smell has been picked up in places including Cuckfield, Brighton, Eastbourne and Worthing and in the southern fringes of Surrey.
Officials at the Lubrizol France factory say the smell comes from a non-toxic additive which gives an odour to natural gas, so there is no danger to the public. There have been reports of people who live near the factory suffering migranes and nausea.
Engineers say they are working to plug the leak and hope to have it fixed by the end of day.
In the meantime, firefighters are advising you to keep your doors and windows closed.
This is the latest from the Health Protection Agency
The smell drifting over Southern England today poses no risk to public health. The odour, which is similar to rotten eggs, has been noticed by people mainly in Kent, East and West Sussex and some parts of Surrey.
It is caused by a particularly smelly chemical that is added to odourless natural gas to give that its characteristic smell.
The chemical leaked from a factory in Rouen, France yesterday and has blown across the Channel overnight. It is not toxic and has also been diluted before entering the air over England, so people should be reassured it will cause no harm. It is an unpleasant odour which may cause some people to feel slightly nauseous but it will dispel naturally.