Emma Bermingham insists that she does not feel desperately sorry for herself. The situation is ridiculous and not great, she continues on the phone, but there are plenty of people who are worse off. She is not talking materially but as I drive up the crunchy gravel to the 1850s pile that is still her home, I can see that you might think that’s what she means.

David is determined to keep the house, she says, refering to her husband David Bermingham, one of the so-called NatWest Three who is awaiting trial in Texas on fraud charges related to the collapse of Enron. She is afraid she is smoking, so we sit outside on the verandah that overlooks a vast lawn leading to an Oxfordshire stretch of the Thames. To our left are tennis courts. It is quite lovely, the fruit of her husband’s successful banking career which is now suspended because of an American legal action that many people believe should never have been permitted by the British Government.

“No other country in the world will extradite its own citizens to a foreign country without a prima facie case,” says Emma. “There’s no way the American Government would do this to its citizens. There would be uproar.”

David Bermingham’s story is told in Taking Liberties, one of many documentaries emerging to assess Tony Blair’s legacy. The theme of this one is that during the past ten years the Government has systematically passed legislation that, in seeking to protect citizens from terrorism, threatens the liberty of all of them.

Bermingham and his co-accused, Gary Mulgrew and Giles Darby, fell foul of the 2003 treaty signed by David Blunkett to enable the extradition, without prima facie evidence, of anyone sought by the US authorities. It was negotiated in secret after 9/11, there was no parliamentary scrutiny of the draft, and it is not reciprocal.

So far, of 60 extradition requests made to the UK by the US, only five have related to terrorism. Forty-six people have been extradited, the NatWest Three among them – even though they are British, their alleged £4.8 million fraud was committed in the UK against a British bank, and none of NatWest, the Crown Prosecution Service, the Serious Fraud Office or the Financial Services Authority (FSA) wishes to prosecute them.

“We are fundamentally unsympathetic people,” said Bermingham before he was extradited. “Ex-bankers who made a lot of money out of doing a deal that turns out to look really smelly.”

The three men maintain that they have done nothing wrong. Indeed, they were arrested only after they contacted the FSA with information that they felt was relevant to Enron. Asked if this could be handed to the US authorities, they agreed, only to find themselves facing charges. Last July they were handed over to American marshals at Gatwick and arrived in Houston in handcuffs and leg shackles. It is believed that they were granted bail only because of the sympathetic British media coverage, and now Bermingham is living in an apartment in Houston, an electronic tag on his leg. The trial is expected to be heard in October.

“The picture of them in handcuffs and leg chains was one thing that I made sure the children didn’t see,” says Emma.

She and David have three children, Jemima, 9, Freddie, 8, and Archie, 5. The family keeps in touch through a free computer service and she has visited David nine times, sometimes with the children. Otherwise money is tight, which seems incongrous in this glorious setting.

“We’re just remortgaging the whole time,” says Emma. “David hasn’t been able to work for the past year. The authorities insist that they get work over there but of course no one will employ them and they haven’t got social security numbers. I looked at a few jobs in shops but I’d be earning less in a month than David is paying lawyers in a day, so we may as well keep rolling up the debt than bringing in peanuts. It’s an awful attitude when you know that everything is costing so much, but at least I’m not as stressed out as I would be and the house is going up in value.

“I’m immensely proud of the children. They back off now – it’s not ‘I want’ any more, they don’t feel the right to have what everyone else has. Jemima had a boy hamster for her birthday and he was £6.50. Freddie said that if we get a girl they can make babies and we can sell them. In their bedroom they make up shops, and they put prices on things and want to take them to the end of the road to set up a stall. They’ve got that entrepreneurial spirit very early.” The daughter of a judge, Emma is poised yet somehow numb. She is 40 and met her husband 14 years ago when she was in marketing and he had left the Army for the City. He pursued her, they married in Brompton Oratory and led a golden life until five years ago when their lives became, as she puts it, surreal. I try to follow her cue about being positive but sometimes she seems unable to answer my questions. She feels tired, she says, and I imagine that remaining positive for her children and her husband must be exhausting. She has told the children that some Americans say that their father has defrauded a British bank and that he has to be in America to sort it out.

“Archie has no real understanding of it, Jemima and Freddie are completely clear. Jemima said it doesn’t make sense – why can’t he go to court in this country? Why can’t they give Daddy a lie-detector test? They’re constantly trying to work things out.”

Emma describes her husband as driven, determined, straight and principled. “He’s not your typical investment banker, he’s a very strong Catholic. He’s one of the lucky ones because most of the other extradited businessmen are in prison, but he is very lonely and fed up. He spends his time going through documents. The three of them are allowed to communicate only in the presence of a lawyer or by e-mail if they copy a lawyer in.

“He has to pay for his tag – it’s something like $9 a day – but the worst thing is that it comes with a huge ‘batphone’ that has to be next to him all the time. If he leaves it anywhere, and it’s so easy to do, the call to the services starts screeching. In America tags are very much associated with paedophiles, and you see everybody looking him up and down.”

The key question remains whether Bermingham and his colleagues will get a fair trial. Their lawyer, Mark Spragg, has pointed out that they are unable to subpoena witnesses who live in Britain, and requests for disclosure of some vital defence documents have been denied.

“The good thing is there’s an end to it,” Emma says brightly. “I can’t think what happens if they lose. I have to think they’re going to win. I’ve told the children that people do sometimes move house and if that’s the worst that happens, I can cope with that.”

— Taking Liberties is released in cinemas nationwide on Friday: www.noliberties.com

Times recommends

• The pink mile: women on death row
• The top 10 richest streets in the world
• Japan's new professional seducers