Guy Fawkes could have changed the face of London if his 1605 plot had not been foiled, explosion experts have said. His 2,500 kg of gunpowder could have caused chaos and devastation over a 490-metre radius, they have calculated.

Fawkes' planned blast was powerful enough to destroy Westminster Hall and the Abbey, with streets as far as Whitehall suffering damage, they say.

Early in the morning of 5 November 1605, Guy Fawkes was discovered in a cellar under the House of Lords with 36 barrels of gunpowder and a 'slowmatch' to ignite the explosive.

He hoped to cause an explosion that would kill James I when he attended Parliament later that day.

The plan never came to fruition, and Fawkes, like the annual population of straw-stuffed effigies, faced a painful execution.

But if he had succeeded, explosion experts believe that King James' death might have been the thin end of the wedge, in terms of collateral damage.