Michael Childs, political campaigner at Friends of the Earth, said: "It is not the type of direct action we would use. I don't think it can be construed as peaceful even if it was a harmless substance.
"Given all the sensitivities around terrorism, it does not do anyone any favours - in fact it could backfire by making protest more difficult in future. We don't want to see Tony Blair chaperoned and kept away from the public in the way the US president is."
He added that the action only resulted in getting Fathers4Justice known as an extremist group. "The Spiderman stunt was more successful because, although it was disruptive, it was non-violent. But this sort of action enables the Government to ignore the issue, because if it is seen to respond directly, it will be seen as condoning the action."
Greenpeace spokeswoman Melanie Hill said: "It's not something we would have done. The throwing of an object is too aggressive."
But a spokesman for anti-nuclear campaign group Trident Ploughshares believed it was an "extremely effective" stunt. David McKenzie said: "People have certainly heard of Fathers4Justice now haven't they?"