The Swiss bank’s back office questioned more than 80,000 incorrectly booked trades as early as August 4, 2011, reports The Telegraph.
But, in a series of emails and telephone calls over the following weeks, Mr Adoboli managed to cover up his allegedly fraudulent trading by confusing accountants investigating the issue.
In one call, Mr Adoboli blamed what he called accounting mistakes on overwork.
“The main problem going through July and August was that we were really, really ******* busy and we had an annoying client which was taking up half my day, plus we had all these client meetings and the market was going crazy, plus I was, like, a man or two down pretty much every day,” he said. “We’re struggling to keep up.”
In another he admitted to causing “a ******* mess, to put it lightly”.
He explained the trades had been either left off the books or incorrectly registered to save time and money. The argument was initially accepted by the UBS accountant who uncovered the problem, William Steward.
However, asked by prosecuting counsel Sasha Wass QC whether he would have accepted the explanations offered by Mr Adoboli as correct, knowing what he now knows, Mr Steward said: “No.”
In detailed testimony the jury was taken through complex explanations about Mr Adoboli’s trading – explanations that left the presiding judge Mr Justice Keith asking for repeated clarifications.
At one point he warned the prosecuting counsel, Ms Wass QC, that he had heard from the court staff that the jury was finding it hard to follow the case.
The full extent of the $2.3bn losses built up by Mr Adoboli were not revealed until September 14 when the 32-year-old investment banker sent his bosses an email admitting making unauthorised trades.
In the email he said: “I take full responsibility for my actions and the stilt [sic] storm that will now ensue. I am deeply sorry to have left my this mess for everyone and to have put my banks and my colleagues at risk.”
In total, Mr Adoboli was discovered to have made incorrectly booked trades worth $3.6bn at the beginning of the August.
On Monday, the court also heard how Mr Adoboli had himself lost £123,000 spread-betting through a personal account with IG index.
His trading with IG Index prompted two official warnings from his bank bosses after he failed to disclose the account and then failed to disclose individual trades.
When UBS banned all its traders from spreadbetting Mr Adoboli continued but with a different account.
Despite being earning £350,000 in the year he was arrested Mr Adoboli owed thousands of pounds on current accounts and credit cards.
His current account showed payments to eight pay-day loan companies including Wageday Advance, Wonga.com and Payday UK.
He denies all charges. The case continues.