Up to 25 people are thought to have been hit by the scammers, including a 66 year-old woman in Perth who had £1500 looted from her account, and a 78 year-old who nearly lost £27,00 after handing over her International Bank Account Number to the fraudsters. On the latter occasion, the bank became suspicious and intervened to stop the transfer of the funds to a bank account in India.

In both incidents, customers were initially contacted by a person claiming to be a Bank of Scotland employee. The caller already had some personal information about the account holders, helping to lull them into a false sense of security.

Tayside Police said it appeared the scammers had managed to tamper with their victim's phone lines, allowing them to divert the call when the women rang back the genuine Bank of Scotland telephone number.

Detective Chief Inspector Bruce Kerr, in charge of the Criminal Investigation Department in Perth, says: "We are working closely with the bank in a bid to track down those responsible.

"I must stress to all members of the public that they should never disclose or confirm any personal information over the phone, particularly bank details. If you have any doubt or any concerns, please go into your local branch personally."