Alternatively Pyongyang, in referring to a "higher level" test, may simply be aiming to test a larger device, substantially bigger than the 1 and 2 kiloton tests of 2006 and 2009.
Mark Winnington, the county's cabinet member for environment and assets, said the project had been costed properly but they were aiming for a "Rolls-Royce job that's going to stand the test of time".