Of all the relationships between major powers, three stand out as having been defined officially as “special”.

The centuries-old relationship between the United States and Britain, the three-year one between China and Russia, and the months-long one between China and Britain.

Global diplomacy has long been dominated by realpolitik, from Machiavelli to Kissinger, though debate rages over whether it is best to base ties on pragmatism or idealism.

It was the British who first summed up diplomatic pragmatism when Lord Palmerston, a prime minister in the 19th century, said: “We have no eternal allies, and we have no perpetual enemies. Our interests are eternal and perpetual, and those interests it is our duty to follow.”

It was also the British who pioneered diplomatic idealism, by building an intimate and harmonious “special relationship” with the US.

The latest special relationship – proclaimed by David Cameron, the former British prime minister, and Chinese President Xi Jinping ( 習近平 ) last October – is an example of diplomatic pragmatism.

It was created in a rush in an effort aimed at short term interests despite deep differences on issues such as human rights, Tibet (西藏), Taiwan, and regional and global security.

The partnership seems short-lived given the dramatic shift by a new British government’s China policy.

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Chinese diplomats have warned Prime Minister Theresa May’s recent decision to reconsider the joint venture over the proposed £18 billion (HK$183.2 billion) Hinkley Point nuclear power station could mean the end of the months-old special relationship.

Cameron and Xi had said the project had elevated Sino-British ties to an unprecedented level and signalled the advent of a “golden era” in relations.

But Britain’s new ‘iron lady’ has never supported her predecessor’s gung ho approach to Chinese investment and has indicated she favours a return to prioritising the country’s ties with Washington.

In contrast, US-British relations are an example of diplomatic idealism. They are rooted deep, going back hundreds of years to before American independence when the seeds of common language, culture, lifestyle, religion and legal theory were planted in the earth of thirteen British colonies.

While the “special relationship” phrase was not coined until 1946, by Britain’s then prime minister Winston Churchill, the existence of special ties was notable during the 19th century, when the two countries’ troops fought side by side in skirmishes overseas.

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Such close ties have endured through the 20th and 21st centuries, with the countries fighting together in two world wars, the Korean War, the Cold War, the Gulf War, and most recently in the ‘War on Terror’.

The China-Russia relationship may sound rosier than the one between China and Britain, as the two have much more in common.

However, it too is based on an alliance of convenience and short-term gain rather than on shared ideas and values.

Economically, Moscow is seeking Chinese capital to offset the impact of Western sanction over its annexation of Crimea and the crisis in eastern Ukraine. In return, Beijing seeks Russian oil. Strategically, the countries share a desire to limit US supremacy.

But despite the influence of communism, the two countries share little in terms of culture, religion, ideology and values.

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Historically, the two have been rivals who have competed for influence throughout Eurasia.

Most observers believe it is the Xi-Putin friendship that drives China-Russia relations. The two strongmen have much in common – personality, ideology and strong nationalistic and anti-West rhetoric.

Xi deliberately chose Russia for his first overseas visit as head of state, announcing the “special relationship” just a few weeks after becoming president in March 2013.

But the China-Russia partnership will face a test, much like the one the China-Britain partnership is facing now, when the two leaders retire – Putin is expected to stand down in 2018 and Xi in 2022.

Then, history might once again show that it is only when diplomacy is built on both common interests and shared values – or a combination of pragmatism and idealism – that friendship between nations can pass the test of time.

Cary Huang, a senior writer with the South China Morning Post, has been a senior editor and veteran China affairs columnist since the early 1990s