Joseph Rayner has not been charged with any offence so far and, under Hungarian law, could be detained for up to a year without charges being brought.
His wife, Desiree, now faces giving birth to their third child alone next month. The baby was not expected when Mr Rayner was arrested and the news was broken to him by his lawyer.
Kim Grady, a British friend who, like the Rayners, lives in Hungary, said yesterday: "He has had no charges, no explanations. When pushed they say he is being held on suspicion of something, but it changes almost on a weekly basis. It is usually something like not paying enough VAT or customs duty."
Mr Rayner, 41, has lived in Budapest for the last eight years, where he runs his own distribution business employing more than 200 people. Ms Grady said he was involved in a customs authority investigation last summer with which he had co-operated.
"He gave them his passport and did what he said he'd do. No one thought it was a big deal. Then last October, Joseph was taken away by customs officers in what I can only describe as a dawn raid. They didn't say where they were taking him, or where he was going."
Although Mrs Rayner expected he would be back by the end of the day, he has been held ever since. Ms Grady said: "In some prisons he has been locked up with convicted multiple murderers. There is no light, he can't sleep. Desiree has gone through a whole pregnancy with this pressure. She's just devastated and so are the children. Their four-year-old son, Daniel, asked if his daddy was dead."
A spokeswoman for the Foreign Office said the Government was doing all it could to help the Rayner family. The intervention of Robin Cook, the Foreign Secretary, secured Mr Rayner one hour of exercise a day. But the Foreign Office was unable to intervene in Hungary's judicial system. "We can't intervene in local laws overseas. All we can do is make sure he has a lawyer, that he is aware of the prison system and the judicial system,"she said.
This angered Ms Grady. "When it suits people, they can make noises. When it's nurses in Saudi Arabia, things happen. But it doesn't have to be the Middle East, or Thailand, for something to be very wrong."
Carlo Laurenzi, director of the international charity Prisoners Abroad, said Mr Rayner's case was not that unusual. "There are ways of holding on to people in countries all over the world, even inside the European Union." He said one man in Portugal had been held in a prison without being charged for more than a year.Reuse content