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The former chief executive of UBS denied on Thursday he was at fault for failing to spot an “epic” interest rate scandal at the Swiss bank despite a former colleague admitting management negligence.

UBS was fined a record $1.5 billion last month for manipulating Libor interest rates, the latest in a string of scandals including a $2.3 billion rogue-trading loss and a tax avoidance row with the United States that have shredded the group's once venerable reputation.

Marcel Rohner said he was “shocked” and “ashamed” when he read about the rigging of Libor interest rates but he said during his period as CEO he was trying to save the bank from collapse and was unaware of the misconduct.

“I did the best I could,” the Swiss national told a British parliamentary panel.

Rohner was CEO for 20 turbulent months between 2007 and 2009, when UBS repeatedly had to tap shareholders for cash as it amassed more than $50 billion in mortgage write-downs. He has not gone back to full-time work since.

Rohner, along with three other former UBS executives, admitted to the committee that they first heard about the bank's role in Libor manipulation in press reports in 2011 despite all four of them being in charge of the investment banking unit for part of the period when the rigging occurred.

Lawmakers blasted the four executives for “blissful ignorance.”

“I'm struggling to see how something of this scale and this central was off radar,” Susan Kramer, a member of the committee, said.

The British financial watchdog said interest rate rigging was so widespread at UBS that every submission it made over a six-year period from 2005 to 2010 inclusive was suspect.

Libor, the London interbank offered rate, is used as a benchmark for pricing trillions of dollars of loans. Even small inaccuracies in the rate affect investment returns and borrowing costs meaning that UBS and other banks implicated in the rigging scandal are at risk from civil lawsuits.

Under persistent questioning, Jerker Johansson, who headed the investment bank for just over a year from 2008, admitted that management had been negligent not to detect the misconduct.

Investigations by British, Swiss and US regulators revealed interest rate manipulation on what the US authorities called an “epic” scale. UBS brokers and managers conspired with brokers to rig the rates to make money and openly boasted about what they were doing in emails and electronic chatrooms. Five internal audits failed to detect what was going on.

More than a dozen banks are under investigation in the Libor probe and further settlements with regulators are expected this year. Barclays paid a fine of $453 million for its role in the interest rate manipulation last year.

Thomson Reuters, parent company of Reuters, has been calculating and distributing Libor rates for Libor's sponsor, the British Bankers' Association, since 2005. - Reuters