Almost a month after after a migration to a new banking platform from parent Banco Sabadell went spectacularly wrong, a number of TSB customers have reported being ensnared by criminals offering to fix ongoing problems with their accounts.

Consumer Website MoneySavingsExpert says it has received dozens of complaints from TSB customers about cash mysteriously disappearing from their accounts followed by desperate hours on the phone trying to contact the bank's overloaded fraud team.

One customer wrote: "On logging on to internet banking I could see that all my savings and bills accounts had been transferred into my current account and then all those funds including my overdraft limit were transferred out.

"I called the TSB fraud line and it took me three hours to get through to them. Once through they freezed my internet banking and cancelled my cards and telephone banking - it was too late by then.

"I’ve called again this morning to chase and it took two hours to get through. Again, no update available. So I’m now in the situation that I have no money, no idea when I might get it back, no cards that work, no internet banking and no telephone banking."

Another said: "I noticed that £9,000 of a loan that I hadn't applied for had appeared in my TSB account. I immediately tried to call TSB - however it took them four and a half hours to answer the fraud line. During this time, I watched as the £9,000 loan and £7,000 of wedding savings were transferred to different accounts. They have said I will hear back within a week."

Forum posters on the site are backing up the claims with their own horror stories.

Action Fraud, the UK police’s dedicated fraud tracking team, says it has detected a significant increase in reports about phishing attacks connected to the TSB IT outage. It appears that criminals targeted irate customers on social media sites during the early weeks of the downtime, pushing them to bogus Websites to input their account details. Once the site was back up and running they then used the harvested data to clean out accounts.

The spike in phishing comes as the FCA’s executive director of supervision for investment, wholesale and specialist firms warned that much of the direct threat to customers from financial crime has moved online.

According to data accrued from 2100 regulated institutions in 2017, phishing and identity theft were cited by firms as the most widespread fraud risks they now face.

"The most rapidly increasing threats - with the exception of malware attacks - were phishing or variants of it," says Butler. "Reflecting the fact that cybercrime now accounts for nearly 50% of all recorded crime in the UK."