He added that he did not think this would offend the American president: "I don't think President Obama minds at all. I think from America's standpoint having a Britain which is more relaxed about its relationship to the U.S. is very important because the U. S. has many other things to focus on."

U.S. President Barack Obama (R) and visiting British Prime Minister David Cameron attend a joint press conference after their meeting at the East Room of the White House in Washington D.C., capital of the United States, July 20, 2010. [Zhang Jun/Xinhua]

The heart of the "special relationship" lay in security, said Niblett, with Afghanistan topping the agenda, as international terrorism from the region posed a threat to both countries.

The economic sphere was almost as important, he said.

Niblett elaborated: "We do have a certain connectivity through our reliance on the finance sector through our commitment to overseas markets and importantly very deep bilateral investment relationships."

A rough ride lay ahead for both countries economically, which would have a bearing on the "special relationship," said Niblett, and in addition would be some serious cuts in British defense spending and therefore its capability to cooperate with America in the military sphere.

"How Afghanistan plays out may have a big impact on how valuable the bilateral relationship is seen at a military level," he said.

And Niblett had noticed fears in the coalition government around American trade policy: "Trade in particular is a big fear, particularly among the coalition government, there's a fear that the U.S. and the Obama administration in particular is less committed to free trade than its predecessors have been. The UK needs free markets to be successful. So, I can see some points of tension in the life of this parliament which may make this pragmatic and rather more mature relationship that we see between President Obama and David Cameron a slightly less special, a more grown-up relationship."

"It could be tested in the next three or four years and any number of areas -- Iran for example. But if I look forward 20 years into the future, I think the UK is going to remain one of the countries with the most close relationship with the U.S. simply because I do not see any alternative for either," he added.