A businessman jailed in the United States for trying to smuggle a key missile component to Iran has returned to Britain to serve out his sentence, his lawyer said Monday.

Christopher Tappin was extradited from Britain last year and eventually pleaded guilty in the United States to attempting to ship to Iran specialised batteries used for the Hawk air defence missile, using false export papers.

He was sentenced in January to 33 months in prison and fined $11,357.

But his lawyer Karen Todner confirmed he has arrived at London's Wandsworth prison after a US judge ruled that he should be allowed to serve the rest of his sentence in Britain.

Todner condemned the conditions in which he had been kept in a New York jail while his transfer was finalised.

"For six weeks while his repatriation was being approved, he was moved to the Metropolitan Correctional Centre in New York, a prison which is teeming with rats and run by gangs," she told the BBC.

"After that, his hands and feet were shackled while he was taken to JFK Airport to be flown home. His family are relieved he is back, particularly as he suffers chest problems."

Tappin, a father-of-two from Kent in southeast England, was caught in a sting operation involving an undercover federal agent.

He had denied attempting to sell the batteries, which were to be shipped from the United States to Tehran via the Netherlands.

But he later admitted that, between 2005 and 2007, he knowingly aided and abetted others in an illegal attempt to export the batteries.