Two men have been arrested on suspicion of money laundering by police investigating an alleged scam by extremists travelling to Syria.
Police said the fraud targeted "unsuspecting vulnerable and elderly victims" who were called at home by a person claiming to be a police officer.
The caller told them their bank account had been compromised and encouraged them to transfer money to an account under the control of the fraudsters.
One elderly man lost approximately £150,000 as a result of the fraud, the Met Police said.
The two men arrested at separate addresses on Wednesday morning were aged 23 and 29.
Six premises were being searched by officers from the Met's Counter Terrorism Command.
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