WikiLeaks distanced itself from the visit by its Australian political offshoot, saying via its official Twitter account on Tuesday: ''Peace brokering a good idea, but [it was] obvious [the] meeting would be spun without care. Did not know or approve.''

The Australian government also expressed anger, with Foreign Affairs Minister Julie Bishop branding the visit ''exceedingly counterproductive'' and ''reckless''.

Mr Shipton said the delegation made the visit because resolving the civil war in Syria - in which an estimated 126,000 people have been killed - was central to world peace and stability.

But he distanced himself from the Assad regime, which among other alleged atrocities is accused of using chemical weapons against its own people. ''He invited us to call in and have a cup of tea, and it was difficult to snub him,'' Mr Shipton said from London.

''We just went along, said hello, didn't say anything much actually … If something is central to the prosperity of the West and the world and could lead to a world war, then you've got to look at it whatever way you can. Our commitment is to peace and the unfolding of the facts and the Syrian people, not to a particular government.''