Mark Summers QC claimed the US had “intruded” on conversations between Assange and his lawyers while he was in the Ecuadorian embassy and the intrusions included “hooded men breaking into offices”.
The WikiLeaks founder appeared in a London court for a hearing on whether he should be extradited to the US to face spying charges.
He reportedly told a hearing earlier this year that he feared he would be kidnapped by the US.
Mr Summers said today those fears are among “multiplicitous” issues that meant the case should be delayed for three months.
He said the case has many facets and will require a “mammoth” amount of planning.
But Judge Vanessa Baraitser denied the request to delay proceedings, meaning the full hearing will be set for five days in February.
Appearing in court today, Assange was clean-shaven and hesitated when asked to confirm his name and date of birth.
He raised his fist in a defiant gesture to acknowledge his supporters in the public gallery, who included former London mayor Ken Livingstone.
Outside the court, more supporters carried placards calling for Assange to be released.
The 48-year-old is accused by the US of conspiring to hack into a classified government computer.
He claims he is a journalist entitled to First Amendment protection.
In June, then-home secretary Sajid Javid signed an order allowing Assange to be extradited to the US.
He has been held in Belmarsh Prison on the outskirts of London while the extradition case is being prepared.
The WikiLeaks founder was due to be released on 22 September but was held for longer because of “substantial grounds” for believing he would abscond.
Assange was jailed for 50 weeks in the UK in May after he skipped bail by seeking asylum in the Ecuadorian embassy in London to avoid extradition to Sweden, where he was wanted in connection with sexual offence allegations.
He was dragged out of the embassy by police in April after Ecuador revoked his political asylum.
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