The US government told Belmarsh Magistrates' Court on 26 February that it doesn't matter whether Assange is wanted for alleged political offences in the US, because they argued the UK-US Extradition Treaty has not been incorporated into English law.
"The accused can derive no rights under the UK-US Treaty", James Lewis QC told the court on behalf of the US. "As a matter of English law his extradition is governed only by the Extradition Act 2003". Lewis argued that because the Extradition Act 2003 makes no mention of an exception for "political offences" then it must mean that Parliament did not want such an exception to exist.
Lewis also cited a litany of English case law to establish that whenever there have been conflicts between international law and English law, English law takes precedence every time.
Article 4(1) of the UK-US Extradition Treaty 2003 states that, "extradition shall not be granted if the offence for which extradition is requested is a political offence".
Lewis argued that even if the court decides that the Treaty does not contradict UK law, but rather works with it and so Article 4(1) is available to the defence to rely on, the charges that Assange faces are not "purely political" so it wouldn't matter anyway.