She was sacked after disclosing that UN peacekeepers went to nightclubs where girls as young as 15 were forced to dance naked and have sex with customers, and that UN personnel and international aid workers were linked to prostitution rings in the Balkans.

After a two-year battle, an employment tribunal ruled yesterday that Ms Bolkovac was unfairly dismissed by DynCorp, an American company whose branch in Salisbury, Wiltshire, dealt with the contracts of the American officers working for the international police force in Bosnia. There will be a further hearing at Southampton to decide the amount of compensation DynCorp must pay Ms Bolkovac.

During her time in Bosnia as an investigator, Ms Bolkovac, 41, uncovered evidence of girls who refused to have sex being beaten and raped in bars by their pimps while peacekeepers stood and watched. She discovered that one UN policeman who was supposed to be investigating the sex trade paid £700 to a bar owner for an underage girl who he kept captive in his apartment to use in his own prostitution racket.

She detailed her findings in a series of explicit e-mails to DynCorp, but after first being demoted and transferred from the investigation she was sacked for allegedly falsifying her timekeeping records.

Charles Twiss, the tribunal chairman, said: “We have considered DynCorp’s explanation of why they dismissed her and find it completely unbelievable. There is no doubt whatever that the reason for her dismissal was that she made a protected disclosure and was unfairly dismissed.”

There are powerful voices in support of her claims, including that of Madeleine Rees, the head of the UN Human Rights Commission office in Sarajevo, who is in no doubt that trafficking in women started with the arrival of the international peacekeepers in 1992.

As well as 21,000 Nato peacekeepers and aid workers, there were police from 40 countries trying to keep Bosnia’s warring factions apart.

“When the civil war ended in 1992 there were curfews and ordinary people didn’t have cars or money,” Ms Rees said. “Only the international community would have been able to get to the flats and bars being made available with foreign women.” She estimates that there are more than 900 premises in Bosnia where sex can be bought.

Richard Monk, a former senior British policeman who ran the UN police operation in Bosnia until 1999, said: “There were truly dreadful things going on by UN police officers from a number of countries. I found it incredible that I had to set up an internal affairs department to investigate complaints that officers were having sex with minors and prostitutes.

“The British officers were on the whole extremely good and very professional, setting a great example. But there were policemen from other countries who should not have been in uniform.”

The tribunal was told that a senior UN official, Dennis Laducer, was caught in one of the most notorious brothels. Mr Laducer, Deputy Commissioner of the International Police Task Force, was investigated by UN human rights officers and is no longer with the mission.

The ruling yesterday will cause further embarrassment to the UN over the behaviour of its peacekeepers. In March investigators disclosed that British aid workers and the UN contingent in Sierra Leone were demanding sex from teenage refugees in exchange for food and money. The UN’s refugee agency, which carried out the inquiry, told of “a shameful catalogue of sexual abuse”.

Ms Bolkovac, a mother of three who now lives in The Netherlands, said that she was elated by the tribunal’s ruling. “Now I hope to gain more international exposure for this problem,” she said.

She was posted to Sarajevo in 1999 to investigate the traffic in young women from Eastern Europe. “When I started collecting evidence from the victims of sex-trafficking, it was clear that a number of UN officers were involved from several countries, including quite a few from Britain,” she said. “I was shocked, appalled and disgusted. They were supposed to be over there to help, but they were committing crimes themselves. But when I told the supervisors they didn’t want to know”. Two Britons, a UN peacekeeper and a policeman, have been sent home after allegations involving the sex trade. Both are being investigated.

Ms Bolkovac said that she witnessed frightened young women given exotic dance costumes by club owners, who told them they had to perform sex acts on customers, including UN personnel, to pay for the outfits.

“The women who refused were locked in rooms and food and outside contact was withheld for days or weeks. After this time they were told to dance naked on table tops and sit with clients, recommending the person buy a bottle of champagne for DM200, which includes a room and ‘escort’.

“If the women still refuse to perform sex acts with the customers, they are beaten and raped in the rooms by the bar owners and their associates. They are told if they go to the police they will be arrested for prostitution and being an illegal immigrant.”

Within days of reporting her findings in October 2000 she was demoted and six months later was sacked. She claimed that DynCorp wanted her removed because her work was threatening its “lucrative contract” to supply officers to the UN mission. DynCorp said that she was dismissed for gross misconduct. During the hearing DynCorp admitted that it had dismissed three officers for using prostitutes. Since 1998, eight DynCorp employees have been sent home from Bosnia; none has been prosecuted.