Residents of Bristol were left baffled and queast by a sinister “gas cloud” that wafted across some of the city’s most expensive suburbs, causing a stink—and a flurry of complaints—on Monday evening.

The south of Bristol, renowned for its leafy avenues and where house prices soar £130,000 above the UK average, was enveloped in a sulphurous odour at around 7pm, with complaints flooding in from areas including Ashton to Bedminster Down, Bishopsworth and Highridge.

The sickening stink grew even more pungent by 9pm. But with the source of this smell a mystery, Wales and West Utilities scrambed engineers to investigate the reports.

The gas company confirmed multiple calls from grossed out resident about the smell. But after a thorough search, insisted it wasn’t related to a leak from their pipes and stated there was no danger to the public.

A spokesperson from Wales and West Utilities pointed to the likelihood of a ‘gas cloud’, caused when smells from industrial or waste processing linger due to stagnant weather and spread across regions, according to Bristol Live. Speculations suggest that the whiff could have emerged from any of the active or extinct waste disposal sites peppering the city’s southwestern outskirts.

“Yesterday (November 11), we received several calls reporting a smell of gas in the BS3 area of South Bristol,” a spokesperson disclosed. “Our engineers visited affected areas and carried out all our necessary safety checks, but there were no readings of gas in the air and this smell has not been caused by a leak from our gas network.”

“However, if anyone ever smells gas, thinks they have a gas leak, or suspects carbon monoxide poisoning, they should call us on 0800 111 999. Trained colleagues will take their call, give them advice, and our engineers will be there to help, day or night.”