Kweku Adoboli, who is accused of making rough bets while working at UBS, had written an email to Will Steward, an auditor at UBS explaining his trading bets that led to the disaster.

Adoboli had out about £7.4 billion of the bank at risk in order to boost his image at the global institution. The trial involving the biggest trading loss in the UK began today. Mr. Adoboli failed to `hedge' the risks for some of the trades in his efforts to boost profits for himself as well as for the bank.

Adoboli has sent a letter to UBS's auditors on 14 September, 2011 explaining that he tried to recover losses but his actions lead to more losses and he was not able to earn back the investments.

"I used the bookings as a way to suppress the PnL [profit and loss] losses that I have accrued through off-book trades that I made. Those trades were previously profit making, became loss making as the market sold off aggressively though the aggressive sell-off days of July and early August," he had written.

He admitted that he did not move quickly to tap the opportunity to unwind smaller losses in the beginning and later he was not able to control the situation that led to the massive loss for the bank.

Sasha Wass QC said that Adoboli gambled away $ 2.3bnof the bank and wiped around 10% or about $4.5bn off the bank's share price.