The Greens have kicked off the party conference season claiming the London bombings were an "entirely predictable response" to the war in Iraq.
Co-principal speaker Caroline Lucas said the situation in Iraq had defied all expectations by getting even worse.
And she criticised "illiberal and draconian" measures proposed by ministers after the 7 July attacks.
"Those of us who state there is a link between Iraq and the suicide bombings are not condoning violence," she said.
Instead it was a question of trying to find an explanation for why 52 innocent people died.
Change of policy?
The MEP told the conference in Lancaster: "The bombs in London were appalling atrocities in which many innocent lives were lost.
"They were also an entirely predictable response to UK foreign policy over many years, but most particularly to our policy in Iraq."
Ms Lucas said that rather than Tony Blair's claim that terrorism was down to "hatred of our way of life", the causes were "injustice and the double standards".
UK foreign policy had to change so it placed "justice and human rights at its heart", she argued.
Chaos in store?
In her speech Ms Lucas also called for electoral reform saying Green voters were being denied a voice in Parliament at Westminster.
And she attacked the UK record on tackling climate change.
"The scenarios painted by the scientists of a world under climate change are a terrifying prospect," she said.
"With Hurricane Katrina in the US we have just glimpsed a fraction of the chaos which lies in store."