A late-night visit by the security contractor who maintained the electronic bracelet around Julian Assange's ankle was one reason why he decided to seek political asylum in the Ecuador embassy in London.

For the first time, Mr Assange has revealed full details of the sequence of events that led to him moving into the embassy last month.

Mr Assange told Four Corners he only took the decision because after a number of "dramatic events" he feared his bail was about to be cut short.

For more than 500 days the WikiLeaks founder had been fighting extradition to Sweden where he is wanted for questioning over alleged sex crimes, including rape.

Speaking from the embassy by phone, Mr Assange said he became suspicious when the Swedish government publicly announced it would detain him "without charge in prison under severe conditions".

What happened next made him believe he may soon be taken into custody.

"On the same evening, the UK government security contractors that maintained the electronic manacle around my leg turned up unannounced at 10.30pm and insisted on fitting another manacle to my leg, saying that this was part of routine maintenance, which did not sound to be credible," he said.

Mr Assange said the following day the security contractor "filed a section nine bail breach against me" in that "my bail would be revoked and they did so under the basis that we refused to let them in at 10.30pm unannounced".

Later that day Mr Assange said he feared his last avenue of appeal was about to be terminated by the British crown prosecution service.

"Acting, we believe, on behalf of the Swedish government, (they) requested that the 14 days that I had to apply to the European court of human rights be reduced to zero."