It is the final day of the Nato summit in Lisbon following agreement to develop a missile defence system to cover all 28 countries in the alliance from long-range attacks and terrorism.

Foreign Secretary William Hague was pressed by John Humphrys as to exactly which threats the system was designed to counter.

"In many ways the world may well become more dangerous over the next 10 or 20 years," argued Mr Hague.

"The missile shield is simply one element of protecting ourselves against a range of possible future threats.

"The idea that we've now gone into some vague period where we don't know what Nato is for, would be wholly mistaken."

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