At the start of the year it was estimated that North Korea would need a decade before they could launch intercontinental ballistic missile with nuclear warheads, Government sources said. That has now been slashed to just a few years.

Sir Michael said he was “very concerned” about the showdown.

He said: “We are doing now what we can to bring about a diplomatic solution. What we have to avoid at all costs is this spilling over into any kind of military conflict.

“We are working flat out at the United Nations to get a better deal there, to reinforce the existing sanctions, we are looking at sanctions across the European Union and of course we are trying to persuade China to keep its neighbour in check.”