Banks must do more to tackle Scams where people are tricked into transferring money to a fraudster, the regulator has said.
This complaint highlighted the problem of "push" fraud whereby victims are conned into paying the wrong person.
However, the PSR stopped short of recommending that banks should be forced to compensate customers.
In response, Which? said that banks had been let off the hook, and they would have little incentive to protect account-holders.
It had wanted banks to refund consumers in cases where customers accidentally transferred money to a fraudster, similar to the protections provided on credit card transactions.
At the moment banks pay up in about a third of such cases. But mostly they do not admit liability, leaving consumers out of pocket.
Such transfers work instantly, and cannot be recalled.
In one example highlighted by Which?, Christopher Mills, from York, was tricked into paying a £10,000 house deposit to a fraudster who posed as his estate agent.
The bank refused to cover the loss.
"Tens of thousands of people have, combined, lost hundreds of millions of pounds to these scams," said Hannah Nixon, the PSR's managing director.
"We need a concerted and co-ordinated industry-wide approach to better protect consumers, and we need it to start today."