An average of nearly £9,000 per case was prevented from being stolen from elderly bank customers owing to a rapid response scheme.
Bank staff have been trained to spot when customers appear to have been targeted by fraudsters pushing scams such as unnecessary home improvements.
Scams totalling an estimated £38m were prevented last year, according to trade body UK Finance.
But consumer groups say risks of complex scams remain.
Fake tax bill
Cases include that of a customer at a branch of TSB branch in Stowmarket, Suffolk, who tried to withdraw £19,000.
Staff noticed the customer was agitated and quietly asked some more questions in a private room. It emerged that the potential victim had believed they needed to pay an urgent tax bill or be fined £50,000 or sent to jail.
The fraudster had called claiming to be an “agent” from HM Revenue and Customs (HMRC) and even suggested the victim make deposits to Bitcoin machines located in newsagents as a way of paying the outstanding bill.
No money was lost, owing to the bank staff stepping in.
Under the protocol, introduced in October 2016, staff are trained to spot the signs of a scam and can request an immediate police response.
A total of 231 arrests and 4,240 emergency calls were made through the industry-wide initiative last year.
The average age of banks’ customers helped by the scheme was 71.
The scheme has prevented £48m of fraud and led to 408 arrests since it was introduced.
However, Gareth Shaw, from consumer group Which? said that overall losses to transfer fraud continued to rise “as people fall victim to increasingly complex scams”.
Meanwhile, reporting centre Action Fraud warned that victims of investment scams reported losing more than £197m last year.
The average loss was more than £29,000, as fraudsters used sophisticated tactics to persuade victims to invest by using fake credentials and contacting people through websites made to appear legitimate.