AS the plane from Ecuador began its descent into the Colombian capital of Bogota, Agent T must have felt a shiver of excitement about her new assignment.

She was being posted to the drugs capital of the world — where she had secured a role gathering intelligence in the war against the global cocaine trade worth £50 billion a year.

An undercover customs officer with Britain’s Serious Organised Crime Agency (Soca), she would be responsible for dozens of undercover agents providing vital information on Colombia’s drugs cartels. The job involved liaising with MI5 and MI6, the British security and intelligence services, and the US Drug Enforcement Administration (DEA).

In her handbag was a memory stick full of secret information that she had personally downloaded from computer systems at her old office, the Soca station in Quito, capital of Ecuador. On it, sources say, were “Soca’s crown jewels” — the names, code names, addresses and operational details of dozens of Soca officers and confidential informants.

After the plane landed at Bogota’s El Dorado international airport in April 2006, Agent T boarded a transit coach to the terminal. She made her way through immigration and then caught a bus heading for the centre of the city and her new office at the British embassy.

For reasons still unclear, by the time she left the airport her handbag — and the vital memory stick — were gone.

It was a blunder of potentially catastrophic proportions. In Colombia, where the drug lords were always trying to keep one step ahead of the authorities, such information was gold dust. Agent T knew that if the data got into the wrong hands it would be a death sentence to those identified.

According to insiders, there was “panic” at Soca’s headquarters in London when Agent T reported the mistake. Her boss, Paul Evans, a former MI6 officer, ordered an internal inquiry, fearing his job was on the line. Agent T was recalled to London to face the music.

A source claims the memory stick contained details of anti-narcotics intelligence compiled over more than five years. The loss risked the lives of undercover agents and informants who have now had to be relocated. He said the total cost of aborted operations was £100m.

“You are talking about years and years of efforts to recruit people prepared to risk their lives to give information on the drugs trade. For someone to have not only possibly compromised all that work, but put many, many lives of individuals at risk, is as bad as it gets,” said an intelligence source familiar with the case.

While officials guilty of similar blunders sometimes face court, Agent T was dealt with behind closed doors at a disciplinary hearing.

With her career hanging in the balance, the agent might have been expected to hire a lawyer. Instead, in a twist that will fuel concern about the handling of the affair, it is understood she turned to an old friend with no security clearance to represent her.

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