North Korean leader Kim Jong Un looks through a pair of binoculars during an inspection of the Hwa Islet Defence Detachment standing guard over a forward post off the east coast of the Korean peninsula, in this undated file photo released by North Korea's Korean Central News Agency (KCNA) in Pyongyang on July 1, 2014. North Korea said it had successfully conducted a test of a miniaturised hydrogen nuclear device on the morning of January 6, 2016, marking a significant advance in the isolated state's strike capabilities and raising alarm bells in Japan and South Korea. REUTERS/KCNA/FilesATTENTION EDITORS - THIS PICTURE WAS PROVIDED BY A THIRD PARTY. REUTERS IS UNABLE TO INDEPENDENTLY VERIFY THE AUTHENTICITY, CONTENT, LOCATION OR DATE OF THIS IMAGE. FOR EDITORIAL USE ONLY. NOT FOR SALE FOR MARKETING OR ADVERTISING CAMPAIGNS. NO THIRD PARTY SALES. NOT FOR USE BY REUTERS THIRD PARTY DISTRIBUTORS. SOUTH KOREA OUT. NO COMMERCIAL OR EDITORIAL SALES IN SOUTH KOREA. THIS PICTURE IS DISTRIBUTED EXACTLY AS RECEIVED BY Image Credit: REUTERS

The newsreaders on North Korean television reserve a special tone of jubilation for announcing nuclear tests. Whenever their youthful dictator detonates the ultimate weapon, the pink-clad lady can barely suppress her glee. She was at her euphoric best on Wednesday, declaring that North Korea had conducted its fourth test with “perfect success” — and, even better, this was the most powerful of the lot! First things first: The regime’s claim to have exploded a hydrogen bomb — the most destructive brand of nuclear weapon — is probably empty bombast.

The earthquake caused by the latest underground explosion at the testing site beneath Hamgyong province was no stronger than the last one in 2013. For now, the experts’ verdict is that North Korean leader Kim Jong-un tried out a hydrogen bomb that fizzled disappointingly — or he let off an enhanced version of an existing weapon. But, whatever the truth, this test delivers two stark lessons: North Korea’s nuclear weapons programme has advanced more swiftly than many predicted — and there is nothing that any outside power, not even China, can do in response.

The latter point appears, on the face of it, the most surprising. Kim is a junior tyrant who inherited the throne of his “Democratic People’s Republic” from his repellent father in 2011. He leads a bankrupt wasteland of a country. And China amounts to his only friend in the world.

Today, North Korea’s regime relies on a drip-feed of Chinese aid. If Beijing were to sever this lifeline, then Kim’s pretensions would be crushed like an irritating ant. When you measure North Korea against the main dimensions of national power, the comparison with an ant does not seem absurd. China’s economy is more than 300 times bigger than North Korea’s; its population, meanwhile, is about 50 times greater. After seven decades of ruin at the hands of the Kim dynasty, North Korea’s entire national output is less than £20 billion (Dh107.1 billion) or the budget of one middle-sized Whitehall department. The spending plans of the Department of Business, Innovation and Skills in 2016 are worth almost as much as the North Korean economy.

Yet, Kim’s weakness is actually his greatest strength. China denounced Wednesday’s nuclear test, just as it condemned all of the others. If Beijing were to cut off the aid, however, this policy would be too successful for its own good. Without a lifeline, North Korea would probably implode and columns of refugees would surge into China. Kim’s grip on power could be imperilled, risking North Korea’s descent from a rogue state to a failed state with a nuclear arsenal on the loose. China, meanwhile, would be deprived of a buffer against American influence via South Korea and Japan.

So the latest test provides yet more evidence of China’s impotence in the face of North Korea’s serial outrages. In truth, this is not a rare phenomenon. A moment comes when the Great Power has invested so much in propping up its horrible ally that changing course becomes too difficult or embarrassing. And the client dictator will always work this out. Back in 1950, China intervened in the Korean War to rescue its friendly regime in the North, losing hundreds of thousands of soldiers. Since then, Beijing has spent billions on North Korea.

Just as America had precious little influence over South Vietnam’s venal rulers in the 1960s, so China has lost its grip on Pyongyang. Kim clearly believes that his neighbour will bankroll his rule whatever he does. And so his nuclear arsenal continues to expand. A decade ago, Kim’s father had four or five Hiroshima-type atom bombs, deliverable only from a vulnerable warplane. Today, his son possesses up to 20 nuclear weapons, perhaps half of which could be loaded on ballistic missiles. Those missiles, meanwhile, acquire ever-longer ranges: The Taepodong-2, currently in development, could fly across continents and strike as far away as the US. So North Korea has crossed the vital threshold from being a country with a handful of primitive atom bombs to one that could actually launch nuclear missiles.

Kim’s next goals will be to work out how to fire his missiles from submarines — allowing them to hit any target in the world while also being immune from a pre-emptive strike — and to maximise their destructive power by developing thermonuclear weapons, also known as hydrogen bombs. Last May, North Korea duly test-fired a missile from beneath the sea; on Wednesday, it claimed to have detonated a hydrogen device. Step by step, Kim is pursuing his nuclear ambitions and no country has the power to restrain him. We can only hope that one day his ossified regime will collapse of its own venality — and that someone will secure his nuclear weapons when this happens.

— The Telegraph Group Limited, London, 2016