The Met Office believes easterly winds could
be carrying the smells
A foul smell detected in parts of England and Wales is being blamed on easterly winds bringing farming or industrial smells across the Channel.
Labelled "Euro-whiff" by the Met Office, the source of the smell - alternately described as sulphur and manure - is under investigation.
The Met Office said it had had hundreds of calls from the public looking for information about the odour.
The BBC News website has received more than 1,000 e-mails about the smell.
Readers have reported a range of sulphur and manure-like smells hanging over large parts of England and Wales.
The Met Office's Sarah Holland said: "Basically, over the last few days, we've had fresh, strong winds from an easterly direction. As a result some of our air is coming from continental Europe."
People sniffing the 'Euro-whiff'
She added that while members of Met Office staff were trying to trace the exact source of the "apparent atmospheric aroma", the likely explanation was either agricultural or industrial works in western Europe.
"Normally, our winds are westerly, coming off the Atlantic Ocean, which bring little or no pollution with them."
Helen Chivers of the Met Office said the origin of the smell had been narrowed down to the area of Europe roughly bordered by Holland, Germany and Belgium.
But, she said, it was unlikely the exact source would be pinpointed.
"I don't think there's any way we will know. The air over that part of Europe has been very stagnant over the past few days, so there won't be any way of telling where it is coming from."
Mrs Chivers said the smell had been described as everything from manure to methane gas to metallic in nature.
Dead animal smell
Some of the strongest smells have been reported in Reading and Basingstoke, with other reports of a stench in East Anglia, as far north as Durham and as far south as Devon.
Forecasters say the easterly winds, which are bringing the current cold front in addition to the bad smell, are expected to last two or three more days.
BBC News website reader Sriram from Stevenage wrote that he feared there might be a dead animal near his house.
"I thought there was something that was dead, like a rat or a cat, and it was their decay that was causing the smell," he said. "I quickly got into the car and drove off, then at the station I parked the car and got out and the stench was still there. I had a serious scare now."
Marian Miller from High Wycombe, Buckinghamshire, said the smell had induced nausea.
"I noticed an acrid smell rather like burning plastic during the night, about 5am. It is the sort of smell you can taste."
Matt from Cardiff said his first thought was to blame the neighbourhood pets.
"I thought it was our local neighbourhood dogs and cats being busy in the night in our garden - but the smell stayed noticeable during my three-mile bike ride to work."
Stu Maddison of Ealing, west London, said he noticed the stench as soon as he stepped out the door this morning.
Mr Maddison said the smell was still in the air when he arrived for work in Notting Hill.
"It's a bit rude really," he said of the air. "Various colleagues thought they'd trod in something but no, it's the air."