Kweku Adoboli, a relatively junior City trader who almost destroyed the banking giant UBS through increasingly reckless illicit deals, has been jailed after being convicted of what police describe as the biggest fraud in UK history.

Adoboli, 32, racked up eventual losses for the bank of over £1.5bn during three years of secretive, off-the-books trades, which he managed to conceal from bosses. At one point, the potential liabilities totalled more than £7bn, a sum described by prosecutors as sufficient to bring down the bank.

The judge, Mr Justice Brian Keith, jailed Adoboli for seven years after the jury at Southwark crown court convicted him on two counts of fraud. He was acquitted on four separate charges of false accounting.

Police and prosecutors sought to portray the Ghanaian-born, British-educated former public schoolboy as an out-of-control gambler who dispensed with the safety net of parallel hedged deals – a requirement that limits profits but, crucially, caps liabilities – purely so he could become a star trader with a big bonus.

Perry Stokes, the City of London police detective chief inspector who led the investigation, said Adoboli was "a young man who wanted it all and was not willing to wait".

Describing the case as the UK's biggest fraud, he said: "To all those around him, Kweku Adoboli appeared to be a man on the make whose career prospects and future earnings were taking off. He worked hard, looked the part, and seemingly had an answer for everything. But behind this facade lay a trader who was running completely out of control and exposing UBS to huge financial risks on a daily basis."

The court heard that despite a combined salary and bonus of £360,000 Adoboli existed in financial chaos, losing £123,000 in a year on private markets-based spread betting and taking out a string of payday loans to cover the shortfall.

However, the judge told a tearful Adoboli he rejected claims that the young trader had been out primarily for personal gain, saying this could also explain the acquittals for false accounting.

But he added that Adoboli seemed "profoundly unselfconscious" of his failings, and should have realised he was being dishonest. He told him: "There is the strong streak of the gambler in you, borne out by your personal trading. You were arrogant enough to think that the bank's rules for traders did not apply to you."

The trial heard Adoboli had had a rapid ascent through UBS after joining as a graduate trainee in 2003. Moving from a back office role to the exchange traded futures desk, he began his illicit deals in late 2008, initially accruing substantial profits. These were lodged in a secret account he called his umbrella and drip fed back on to the regular books. But as European markets hit turmoil in the summer of 2011, the trades began to make a loss, which he desperately attempted to recoup with ever-bigger punts.

As the losses mounted, UBS's back-office accountants pressed Adoboli on apparent anomalies. Soon after midday on 14 September last year, Adoboli walked out of the bank's headquarters and returned to his east London loft apartment to compose an email that accepted "full responsibility for my actions and the shit storm that will now ensue", also apologising for having put the bank at risk.

The email, and Adoboli's acceptance that his actions cost UBS such as vast sum, could have indicated that his decision to deny all charges was misguided. But giving evidence, he insisted his colleagues had known about the umbrella, and said UBS bosses placed him under enormous pressure to increase profits, whatever the means.

The accumulated testimony was deeply damaging for UBS, which lost its chief executive after Adoboli's arrest and is being investigated by the Financial Services Authority and the equivalent Swiss watchdog over apparent control failures.

All three of Adoboli's desk colleagues admitted they knew about the secret account, to varying extents, and his two bosses over the period showed an apparently relaxed attitude to daily trading maximums being exceeded. All five have either left UBS or been sacked.

Against this drip-feed of bad publicity UBS fielded several court benches worth of firepower: there every day were a varying lineup of solicitors from the City law firm Herbert Smith, the leading fraud barrister Allison Clare and a phalanx of phone-wielding PR enforcers who intermittently harangued reporters during breaks if they disliked what had been filed.

UBS said in a statement: "We are glad that the criminal proceedings have reached a conclusion and thank the police and the UK authorities for their professional handling of this case. We have no further comment."

Despite the regular technical jargon, much of which arose from Adoboli's sitting with his legal team so he could consult with them rather than being in the dock, the nine-week trial was rich in compelling human drama. A devastating opening speech by the lead prosecution barrister, Sasha Wass QC, portrayed Adoboli as a narcissistic status-chaser whose hubris compelled him to try to claw back his losses with ever more reckless bets. She said: "Like most gamblers, he believed he had the magic touch; like most gamblers, when he lost, he caused chaos and disaster to himself and all of those around him."

Adoboli himself wept copiously and frequently as he began his testimony, telling the court how he felt betrayed by an employer to whom he had been so dedicated he missed his grandmother's funeral to remain at his desk.

He painted himself as a man culpable but also wronged, expressing remorse over the losses. However, he added: "I'm devastated. But in the end, the reason I'm most sad is because these losses weren't the result of dishonesty or fraudulent behaviour. It was the result of a group of traders who were asked to do too much, with too little resource, in a market that was too volatile."

It is telling that the jury and judge, if not police, accepted this explanation, at least in part. Given a 50% tariff reduction and time spent on remand or under curfew, he could be out of jail in just over two and a half years' time – which would work out as one day in prison for each £1.6m in losses.