John Everard said the reclusive regime still has a trick up its sleeve as it is yet to test its rumored miniaturised nuclear war heads.
Commenting on recent war fears sparked by a North Korean missile launch, he told Sky News: “I think people are probably more worried now that the North may be proceeding towards not a further missile launch but a sixth nuclear test.
“Remember that they have claimed to miniaturise nuclear war heads, make them small enough so that they can actually fit them on top of their missiles.
“They haven’t actually tested one of the miniaturised ones yet. So that’s a treat in store.”
Mr Everard said North Korea had shot a missile over Japan as a warning to the United States after President Donald Trump promised he’d hit Pyongyang with “fire and fury” in the event of an attack on the oversea territory of Guam.
The diplomat, who served in North Korea from 2006 to 2008, said North Koreans were “shaking up” Japan because it is a key ally of the United States.
He said: “It’s important to understand we are not going round in circles: we are going down a spiral.
“At the end of each of these iterations, the situation is tenser and tenser. Now we’ve actually seen North Korea fire a missile over Japan. This is really not good.
“The world goes on but the world is a much less safe place now than it was yesterday.”
In a written statement, President Trump said that now “all options are on the table” in terms of a US response to the latest Kim Jong-un power trip.
The recent test prompted the United States, alongside Japan and South Korea, to call for an emergency meeting of the United Nations Security Council.