People living in Letchworth are scratching their heads over a spot of bother that has been landing on their cars, bins and washing lines.

The mustard-coloured solution, which lands as liquid but soon hardens into powder on ground-based surfaces, was first spotted on cars in Kristiansand Way in late August, but has since been discovered in North Avenue, Common View and Glebe Road.

People living in the area have conducted an investigation and also found spots of the solution on Blackhorse Road, Green Lane and Norton Road.

Roland Talbot, of Kristiansand Way in Letchworth, said: “Kristiansand Way and its close neighbouring roads appear to be hit much worse that other areas.

“The may be because of its natural height, being the highest point both in Letchworth and the shire.

“The marks do not appear to burn into paintwork in any way. However they do spoil any fabrics like washing left outside on a line.

“We want to get this sorted out once and for all.

“We do not appear to get any occurrence during the night but it does start very early in the morning. Additionally we do not get any occurrences during weekends. It is difficult to say if changes in weather conditions could affect it.

“At this stage residents are collating information to allow North Herts’ environmental health team, which is investigating, to run tests to see if the solution is harmful and detect where it comes from.”

Councillor Bernard Lovewell, responsible for housing and environmental health for North Herts District Council said: “Our environmental health team is investigating to try and find the cause.

“There is no evidence that this is any form of industrial pollution and at the moment we are focussing on some sort of natural cause which doesn’t have any public health significance.”