Britain's process for deciding whether to agree to a US extradition request for WikiLeaks founder Julian Assange is likely to take up to a year and could be complicated by the renewal of a separate Swedish extradition request, lawyers say.

The process began with a few brief formalities on Thursday, when Assange appeared by video link from prison to confirm that he opposes his extradition to the United States.

The US Justice Department said it charged Assange with conspiring with former US military intelligence analyst Chelsea Manning to leak classified material in 2010.

Another procedural meeting is scheduled on May 30 before lawyers for the US government and Assange present their initial arguments for and against his extradition at the start of the formal hearing on June 12.

A judge in an extradition case must be satisfied that ‘the [alleged] conduct amounts to an extradition offence’ and examine any possible bars to handing over a suspect, including whether extradition would breach the person's human rights, according to British government guidance.

‘If the judge is satisfied that all of the procedural requirements are met, and that none of the statutory bars to extradition apply, he or she must send the case to the [home secretary] for a decision,’ it says.

Assange would have the right to appeal the decisions of both the judge and the home secretary.

British human rights lawyer Karen Todner, who specializes in extradition, told dpa she expects Assange's legal team to make at least four arguments against him being handed over to Washington.

They include the ‘political motivation’ of the arrest warrant, concerns over US prison conditions, the possibility that Assange could serve life in prison without parole, and his mental and physical health.

Ecuadorian President Lenin Moreno said Britain had assured him that Assange would not be sent to any country where he could suffer ‘torture, ill-treatment or the death penalty.’  ‘The United Kingdom extended written guarantees that if extradition is eventually requested he will not be extradited to any country where [he] may suffer such treatment,’ Moreno told The Guardian newspaper.

Todner said she also expects Washington to give an assurance that Assange will not be subject to the death penalty if he is extradited.

Extradition could also be prevented if Assange's lawyers can successfully argue that he is mentally or physically unwell, she said.

‘I think being in the same room for seven years has probably had some toll on his mental health, and I am sure his lawyers are having him psychiatrically and physically assessed to see if he is well enough to be extradited,’ Todner said, referring to Assange's asylum in the Ecuadorian embassy in London from 2012 to April 11, 2019.

She said the judge will consider the provisions of English law, a bilateral extradition treaty between Britain the United States, and international human rights conventions.

‘A Swedish extradition request could definitely complicate the process, particularly if Sweden decides to resurrect the warrant that they presently have outstanding as that would possibly be taken as a priority over the American request,’ Todner said.

The 2010 Swedish extradition request concerns charges of rape and sexual assault, which were later dropped. Swedish prosecutors said last month that they will re-examine the rape case.

If Home Secretary Sajid Javid were to give a renewed Swedish extradition warrant precedence over the US warrant, as some British lawmakers have urged, the whole process could be completed in a few weeks since the time limits for appeal have expired, Todner said.

‘In relation to the American warrant, if that is the one that takes precedence and goes forward, I think the whole proceedings will probably take about a year,’ she said.

Related Story