Celebrity backers of Julian Assange have lost £200,000 in bail money they put up for the WikiLeaks founder, it has been confirmed.

At a hearing at Westminster magistrates court on Tuesday, district judge Howard Riddle adjourned a further hearing until October to decide whether nine other backers should also lose their money, after Assange fled an attempt to extradite him to Sweden last June.

At Tuesday's proceedings, a court clerk told reporters that a £200,000 security pot given to the court before Assange was bailed – and believed to have been paid into by high-profile backers, including Jemima Khan, film directors Ken Loach and Michael Moore, and millionaire publisher Felix Dennis – had been forfeited at an earlier hearing in July.

Assange skipped bail in June and took refuge in the Ecuadorean embassy in Knightsbridge, London, in defiance of an order to have him extradited to Sweden to face allegations of rape. He has claimed the Swedish extradition request is a ruse to facilitate his onward extradition the US, where he could face the death penalty.

Last month Ecuador's president, Rafael Correa, granted him asylum and said the 41-year-old Australian could remain at its London embassy indefinitely.

Journalist Phillip Knightley, Caroline Evans – the wife of former Labour minister Lord Evans – Nobel prize-winning biologist Sir John Sulston and Frontline Club founder Vaughan Smith, who also allowed Assange to stay with him at his Norfolk mansion during extradition proceedings, were among those who pledged sureties – a promise to pay the court – of £20,000 each. All nine of those listed in Tuesday's hearing had pledged a total of £140,000. All in all, Assange's backers could lose £340,000.

Adjourning the hearing until 3 October, Riddle said those guaranteeing bail had a month to persuade Assange to surrender to police if they wanted their money back.

"At the moment I'm not persuaded that any reasonable surety would not be using every effort, publicly and privately, to persuade Mr Assange to surrender himself to UK authorities," he said.

He said it found it "absolutely striking" that none of the nine had attended court in person.

Henry Blaxland QC, representing four of the sureties, said Vaughan Smith was making a documentary with the British army in Afghanistan, while Evans is on holiday in Italy.

The judge noted that "we have no explanation from others and no particular reason to believe that they want to be here".

Blaxland argued there was "no evidence that any of the sureties are to blame for Mr Assange's failure to surrender" adding that the event could not have been predicted by those putting up bail money.

"It was an extraordinary thing to do. Nobody could reasonably have foreseen that's what he would do," he said and urged that the hearing be postponed indefinitely.

"Given the drama at the Ecuadorean embassy has not yet reached the final act, perhaps one should wait to see what does happen," Blaxland said.

Blaxland also argued that since Ecuador had granted him asylum the court should "consider in deciding whether his failure to surrender to police is wholly unreasonable".

Riddle initially refused the adjournment but later allowed a further three weeks so the sureties had a chance to fight for their money.