The campaign, which will also feature on the Tube, is backed by the British Humanist Association and prominent atheist, Professor Richard Dawkins.

BBC: Atheists launch bus ad campaign

He also mentioned the atheist Professor Richard Dawkins, whose comments about the Earth's diversity Dr Williams said reflected the feeling of the Spanish saint, St John.

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The festival takes place in Salford, Greater Manchester, on Wednesday and Thursday and will include a debate on the relationship between science and religion between Professor Richard Dawkins and the country's Chief Rabbi, Dr Jonathan Sacks.

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