A terror suspect who is believed to have travelled to Syria received money from a £600,000 scam which targeted elderly people’s life savings, according to police.

Four men have been convicted of conspiracy to commit fraud over the scam at the Old Bailey and remanded in custody before sentencing in the new year. They posed as police officers to target victims in their 70s, 80s and 90s and convince them to hand over money.

The fraudsters told their victims their savings were in jeopardy and advised them to transfer money or hand over cash for “safekeeping”, when in reality they were being ripped off.

Commander Richard Walton, the head of the Met’s counter-terrorism command, said the scam had been uncovered after a 10-month investigation by anti-terror detectives. “We uncovered this fraud after a separate terrorist investigation found suspicious payments into a bank account of an individual who is now believed to have travelled to Syria,” he said.

After police linked the gang members together, Walton continued, a fraud on a huge national scale emerged involving 5,695 calls to 3,774 different numbers across the UK. Mohamed Dahir, 23, Shakaria Aden, 21, Yasser Abukar, 23, and Mohammed Abokar, 28, were found guilty of conspiracy to commit fraud between May last year and May this year. Ibrahim Farah, 23, was cleared of the same charge.

Mohammed Abokar was also convicted of converting criminal property – £9,000 belonging to Nanette Goldthorpe – on or around 29 January this year.

After the verdicts, Dahir’s barrister Patrick Harte said that the Islington North MP, Jeremy Corbyn, had sent a letter as part of his bail application in May, saying that the defendant had “roots in the area”.

The Labour leader’s name was referenced by Harte in a bid to convince the judge to allow Dahir to remain on bail despite being found guilty at the Old Bailey.

The gang targeted at least 18 victims from across the UK. One victim, an 84-year-old woman, fell victim to the scam after being told she needed to move her life savings for safekeeping. “She received a phone call from a person pretending to be PC Hopkins from Hammersmith police station,” said the prosecutor, Kevin Dent.

“‘PC Hopkins’ told her she needed to go to the bank immediately to transfer the money to keep it safe. She was threatened that if she did not comply she would lose her entire life savings.”

The fraudsters arranged a taxi to go to the woman’s house in Barnstaple to take her to Lloyds Bank. But staff there became suspicious when she became so confused she tried to transfer the money with her Sainsbury’s loyalty card, the court heard.

Another victim, a 70-year-old man from Weymouth, Dorset, was conned out of £113,000 by a fraudster posing as “DC Adams” from Hammersmith police station. He was told that his life savings were at risk from an “inside job” at the bank and instructed to transfer them into 11 separate accounts operated by the gang.

“This is a fraud that preys upon people’s frailty, vulnerability and isolation,” Dent said. “These defendants and some others acted together to commit fraud against mostly elderly people, doing their best to remove from their victims as much as they possibly could.”

Walton said that police were continuing to investigate and would seek to arrest and prosecute anyone else found to be involved.