Citigroup, the US financial services giant, has revealed in a leaked internal memo that it 'regrets' making €15bn trades in government bonds last month which landed it at the centre of investigations by seven European regulators.

In the memo, obtained by Financial News Online, Tom Maheras, head of global capital markets described the trades as "innovative" but said: "However, we did not meet our standards in this instance and, as a result, we regret having executed this transaction. Unfortunately, we failed to fully consider its impact on our clients, other market participants, and our regulators."