Stories circulating that the elaborate scam is being operated outside Asda's popular Kirkland Street store have even prompted police to investigate and local councillors to issue warnings in their official minutes.

The report suggested that opportunist crooks, posing as perfume salesmen, were spraying young female shoppers with a drug to subdue them before robbing them.

After spending time at the 'crime scene', officers quickly deduced the supposed scam was nothing more than an urban myth.

A force spokeswoman said: "We first received a call about this in March and have sent officers out on patrol to investigate but there is no evidence of it ever happening.

"Our Neighbourhood Inspectors will link in with Asda staff if there are any further reports – but there haven't been any more so far."

Far from being the end of the matter, the issue has even featured among the minutes of July's meeting of Windle Parish Council.

Windle Parish Councillor Sheila Barton picked up on the rumour in an e-mail conversation with a friend and alerted her fellow councillors.

She said: "I was told that these scam operations had been taking place down south and that a copycat scam had happened here as well.

"Regardless of whether it's happened in St Helens or not I just wanted to send out a general message for people to be in their guard. There's nothing to say it can't happen here.

"Apparently, robbers approach young women when they're getting in their cars and spray them with a drug which knocks them out before stealing their handbags."

However, not everyone at the meeting was convinced, with fellow Windle councillor Nancy Ashcroft dismissing the perfume story as apocryphal.

Asda, meanwhile, have backed the police's verdict.

"The safety of our colleagues and customers is paramount and we take even rumours very seriously," a store spokesman said.

"Our customers should be reassured that this isn't happening in our car park and our security team is working with the local police and neighbourhood watch to keep our customers extra safe."

* This isn't the first time word of mouth has spread apparently false rumours in St Helens.

In recent years, residents have reported sightings of a giant rat prowling the streets of St Helens – but no firm evidence of the beast's existence has ever materialised.

In years gone by there were also spook stories about vicious dwarfs inhabiting a labyrinth of caverns in Crank.

Other apparent hoaxes on Merseyside include an urban myth about
criminals planting needles in cinema seats in Liverpool. No evidence of the practice taking place has ever been found.

St Helens biggest supposed urban myth actually turned out to be real. For years, youngsters scare each other with tales of the bogeyman Purple Aki. But in 2002, Aki was jailed for a string of crimes.

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