Ben Gregory, 26, believes his drink was spiked during a night out in Clapham in south London.

Criminals then stole £18,000 using financial apps on his smartphone.

A leading campaigner in the fight against fraud says Ben's case appears to show fraudsters adopting the "sinister" tactic of spiking drinks to steal money from victims.

David Clarke, chair of the Fraud Advisory Panel charity, says people need to be alert to the dangers this Christmas party season.

"Fraudsters are cruel, devious people online and in the physical world and people must be alert to the danger of having drinks spiked especially in the Christmas party season when people may be off guard."

'Alarm bells started ringing'

Ben was on a night out with friends in the summer which went from a nice meal out, to a nightclub... before he woke up late the next morning unable to remember anything.

"I remember waking up... with no phone or wallet," he says.

"I woke up pretty dizzy, dazed, not quite sure what happened so obviously I was a bit alarmed.

"I had some messages on my work phone from my brother saying: 'Is everything OK [because] there's been an overdraft opened on our joint account. What's happened?'.

"As soon as I saw that alarm bells started ringing because I didn't do that."

Spiking people's drinks is more commonly associated with men targeting women and with sexual assault as the motive.

But in Ben's case he believes criminals had targeted him with the intention of both defrauding and stealing from him.

Over the space of just a few hours dozens and dozens of transactions, transfers and withdrawals were carried out using Ben's phone and cards.

Two, separate, £2,500 overdrafts were created on his accounts and money in his savings accounts was transferred to current accounts and then withdrawn.

In total, just over £18,000 was stolen from his American Express and Revolut cards and from HSBC and Monzo accounts.

"I felt terrible, absolutely terrible. Over the next few days I couldn't stop thinking about it, couldn't sleep, found it very hard to eat. Because ultimately I felt worried and vulnerable."

Police investigating Ben's case say they have made several arrests.

Inspector Dave Laurie, who works for London's Metropolitan Police, says many incidents of people having their drinks spiked, whether with sexual assault or theft/fraud as the motive, go unreported due to things like embarrassment or memory loss.

"[Spiking] is a terrible thing that's happening and it goes further than the impact on the individual. This impact will run deep. And we know many spiking incidents will go unreported," he says.

"There are ways we can try to help stop spiking happening in the first place.

"Buy your own drink, watch it being poured, don't accept drinks from strangers, never leave it unattended. If your drink doesn't taste right throw it away and get another one."

How common?

Despite lots of calls to police forces, charities and other organisations it's impossible to know how common spiking fraud is.

But David Clarke from the Fraud Advisory Panel says even if it is rare the consequences for victims are very real.

"We need big tech and big finance to come up with big solutions to this type of fraud, " he says.

"Yes individuals can try to help themselves, but there is a limit to what people can do.

"We need technology to help because the crooks are so advanced."

As for Ben, American Express and Monzo refunded the money that was stolen within a matter of days. HSBC and Revolut initially refused to refund but reversed that decision once Money Box started investigating the case.

HSBC said; "We have thoroughly reviewed this case, and in light of new information we will be providing a full refund to Mr Gregory.

"While we have an experienced team looking for signs of fraud, as this case sadly highlights, scammers are unscrupulous criminals who use a range of techniques to exploit their victims. We encourage people to be on their guard."

Revolut said; "This was an unusual case where the payments were authorised by the customer but, as is now clear, without his consent. We very much regret the distress and inconvenience to Mr Gregory and we have reimbursed his losses."