A retired British businessman accused of conspiring to sell missile parts to Iran was extradited to the United States on Friday, but branded his treatment a "disgrace".

Speaking to reporters as he arrived at London Heathrow airport, where he was taken into custody by US marshals, Christopher Tappin protested his innocence and said he should have been tried in Britain.

US prosecutors accuse the 65-year-old of attempting to unlawfully export batteries for surface-to-air missiles, which were allegedly due to be shipped from the US to Tehran via The Netherlands.

Tappin fought a lengthy battle through the British courts against his transfer to the United States, where he could face 35 years in jail, but lost a final appeal to the European Court of Human Rights last week.

Accompanied to Heathrow by his tearful wife Elaine, Tappin said he was "not very confident at all" about the outcome of his case.

"If I wanted anything, it was to be tried in the UK, not in America, because the Americans have never had to produce one piece of evidence," he said.

His lawyer Karen Todner said: "Mr. Tappin has been taken now by British extradition officers to the airplane, where he is going to be handed over to US marshals.

"He will be arriving in El Paso (Texas) this afternoon. He will be appearing in court on Monday morning, so he will be in custody over the weekend."

The British media have highlighted Tappin's case as an example of what many view as the unequal extradition arrangements with the United States.

Critics says US authorities have to provide far less information about an alleged crime to secure the extradition of a Briton than British authorities must provide to extradite an American.

Prime Minister David Cameron said this week that ministers would carry out a review of the arrangements, but said a recent report had found no need for fundamental reform.

Tappin compared his case to that of cleric Abu Qatada, once described as Osama bin Laden's right-hand man in Europe, who has been fighting extradition from Britain to Jordan on human rights grounds for more than six years.

"If I was a terrorist I would not be going to America. I think it's a shame, a disgrace," he said.

Tappin has argued that he was caught up in a US customs sting.

He says he believed he was exporting batteries for the car industry in The Netherlands, but US authorities say he also told customs officials his shipments were destined for an oil company in Norway.