In this US lawsuit, a civil subpoena has been issued by a US court and a request been made to the relevant UK court for them to compel Assange to answer a list questions. If the UK court agrees to the request then the interview would take place within the UK using their civil procedures and laws that apply.
Off topic I know but earlier this year, I read about a law suit settled in the UK that referred directly to language in the Magna Carta as the governing law.
Good stuff. Thanks.