A smell of rotten eggs reported by people in Sussex and Surrey is of no risk to public health, according to authorities.
The gas-like odour has leaked from a factory in Rouen, France, and is caused by a particularly smelly chemical that is added to odourless natural gas to give that its characteristic smell.
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.
West Sussex Fire and Rescue Service asked that people only call them unless there are genuine reasons to suspect a gas leak.
For public health information call the Health Protection Agency South East Communications team 01403 229074, 01403 229075 or 07789 295454