Police in Hackney are pushing for banks to change policy after staff at Santander allowed a vulnerable pensioner to leave its Dalston branch with £49,000 in bank notes rammed into a carrier bag.

Marjan Warren was conned out of a massive £149,000 in the sophisticated and elaborate scam, which saw fraudsters pose as police officers. The bank has pointed out it is legally required to release cash if asked, but says it gave Marjan information about scams first, and had the transaction checked by a senior staff member.

Crooks managed to convince Marjan, 74, from South Hackney, that her bank and financial adviser were part of a criminal network connected to terrorist financing. Over the course of a month, callous thieves ordered Marjan – who believed she was working in an undercover police op – to withdraw her life savings from Santander and Halifax and picked the money up by courier.

Marjan, whose husband died six years ago, was also told to buy £42,000 worth of jewellery in Harlesden, also taken by courier.

Marjan initially didn’t believe the con artists when she received their first call out of the blue. But after they told her to call 999 to verify their story she felt confident she was speaking to police – not realising they had kept the line open and she was speaking to an accomplice.

She only realised she had been scammed after confiding in a friend what had been going on.

“I really didn’t believe my neighbour when he told me it was wrong,” Marjan told the Gazette. “They had me so in the palm that I was really thinking that I was helping them.

“But then I started to think: ‘Oh, my goodness, I’ve done something really silly stupid.’ Those people are really convincing.

“I would like to let as many people as possible know that they need to be very careful who they answer the phone and the door to.”

Police have done everything they can to recover the money, but the criminals are untraceable.

Hackney CID now wants to introduce an industry-wide intervention to stop similar scams from getting this far. If a person wants to withdraw more than £25,000 in cash they say the bank must have a meeting with them where they ask if people are being defrauded.

But the fraudsters are clever, said Det Con Samuel Freeman. “They know this will happen. Victims are conditioned to not believe anything the banks say.

“But at that point the victims can be given a leaflet from police asking if this set of circumstances is happening to you. That might be something that the victims will believe, or at the very least they might think: ‘Let’s call 999.’

“Because fraud is so difficult to trace, the best thing is to target the victim and prevent them believing it in the first place.”

Hackney CID will roll out the scheme locally and hopes the industry might take it further if it works.