Gunpowder plot blast 'would have destroyed' Westminster

Guy Fawkes' gunpowder plot would have wrecked buildings in Whitehall up to a third of a mile away as well as destroying the Houses of Parliament and Westminster Abbey, scientists have calculated.

By working out the explosive power of the 2,500kg of gunpowder he secreted under the old Westminster Hall in November 1605, physicists at the Centre for Explosion Studies at the University of Wales, Aberystwyth, forecast there would have been "severe structural damage" from the blast.

The calculation is the first time anyone has worked out what could have happened if Fawkes' plot to blow up King James I, as he addressed Parliament in the House of Lords on 5 November, had not been discovered the previous night.

The scientists at Aberystwyth assumed the gunpowder would have had the same effect as the equivalent weight of TNT let off above ground.

Dr Geraint Thomas, head of the centre, said: "From the amount and placing of explosive, we can work out that, if you are a third of a mile away, you should be OK with just a few broken windows around you. Further away and you might have just heard some noise."

The key to figuring out the damage is calculating the intensity of the air pressure pulse released by the explosion. "From that we can tell if windows are going to be smashed or whole buildings will be demolished," Dr Thomas said. He added that, even though gunpowder would not be as efficient as TNT, if the barrels were well packed it could have been almost as powerful.