THE origins of a rotten stench in York remain a mystery.

Residents in much of the city woke up to what was described as a “farmyard smell” yesterday morning, causing several of them to phone the council.

The pong could be smelled throughout the city centre and west York, with descriptions of it varying from sour milk to a cowshed.

Three possible culprits have now been proposed – farmers spreading manure on surrounding fields, Harewood Whin tip or temperature inversion.

A spokeswoman for City of York Council said the authority had received a number of complaints yesterday morning about the smell.

Two employees were then sent out in a car to try to track down the source of the whiff, and believed it was emanating from Harewood Whin in Wetherby Road.

The spokeswoman said the council had passed the issue onto the Environment Agency.

But the agency said it had received no complaints about the waste facility.

Another reason for the odour was proposed by the University of York’s environment department.

Prof Mike Ashmore said he thought the problem was caused by a temperature inversion. This means the cold air overnight was trapping the fumes produced by rush-hour traffic because the sun had not had chance to warm the atmosphere sufficiently.

In an effort to track down the origin of the odour, The Press also contacted the National Farmers’ Union.

A spokeswoman said slurry would not be put on fields until the spring, but farmers did spread manure at this time of year.

She said chicken manure was particularly potent, but had no way of ascertaining whether the smell was caused by that combined with a prevailing wind.