Nationwide is calling for changes to the banking code to ensure that savers are informed when introductory deals come to an end.
The building society says many introductory deals, often lasting between six and 12 months, offer rates up to 1 per cent higher than the ongoing rates when the deals expire.
The banking code is currently being independently reviewed and a response from the banking industry is expected this autumn.
Savings director Matthew Carter says: “On the face of it, these rates may look very attractive to savers looking for a good return on their money but beneath the surface they are often little more than a smokescreen hiding an account paying a lower rate of interest.
“A few weeks before an introductory deal coming to an end, savers should be told by their provider when they can expect to see a change in their interest rate, as well as details of the new rate they will receive.”