"It’s becoming clear that… you can no longer expect fair treatment from British law if you sign contracts in London and in the UK," John Shipton said in an interview with the RT broadcaster.
Assange took refuge at the Ecuadorian Embassy in London in 2012 after a British court authorized his extradition to Sweden on rape and sexual assault charges. Assault claims were later dropped.
The whistleblower fears that Sweden may hand him over to the United States to be prosecuted for espionage after his website leaked classified US data.
A UK government spokesperson said Friday that Assange was voluntarily avoiding lawful arrest on the outstanding allegation of rape so the United Kingdom would continue to have a legal obligation to extradite him to Sweden.