Andrew Tyrie told Radio 4’s Money Box programme yesterday he would be writing to Stephen Hester, the chief executive of the bank to express his concerns and seek answers over its unsecure banking technology, reported the BBC.

NatWest only recently launched Get Cash, along with another system called Emergency Cash, which involves calling a phone operator. Both systems generate a security code allowing customers to withdraw money from cash machines without a card.

However, BBC Radio 4’s Money Box programme discovered that some customers had fallen victim to fraudsters, losing thousands of pounds through the Get Cash app.

Last week, NatWest promised to refund losses and suspended the app.

Andrew Tyrie MP said: “It seems possible that all NatWest customers may be vulnerable to this type of fraud even if they haven’t asked to take advantage of this new system.”

“Before they introduce these systems, they really have to be very sure they’ve buttoned up the fraud risk, but in this case it appears that didn’t happen.”

Tyrie said: “It looks as if the bank was slow out of the traps to deal with this.”