Calls to the Serious Fraud Office’s whistleblower hotline have failed to lead to any official investigations.
The "SFO Confidential" service received over 2,700 calls about complex fraud or corruption in 2012.
However, the fraud body decided to close the phone service last June as a “disproportionate amount of staff time was being spent dealing with telephone calls”, according to City A.M.
The "SFO Confidential" service has now been scaled down to allow tips by email and online forms.
The news emerged as the SFO intends to bring charges against individuals in the banking sector within months over the Libor rate rigging scandal.
"We will go where the evidence takes us, but we will always want to focus on more senior people and those with the greatest culpability when we can," an SFO spokeswoman said.
"We anticipate making the next charging decisions [against individuals] in the Autumn."
The furore surrounding the London interbank offered rate (Libor) has led to three banks, Barclays, the Royal Bank of Scotland and UBS, paying around $2.6 billion so far in settlements with British and American regulators.