Heads of government can rarely resist the lure of foreign affairs. Back in 1979, Margaret Thatcher had a large and troublesome economic agenda, which seemed likely to consume all her energies. She made time for abroad. Not long before he became Prime Minister, Tony Blair had lunch with the heads of MI6, and left them feeling gloomy. He appeared to believe that any non-European aspects of foreign policy were outdated and irrelevant. That changed. George W. Bush came to office scarred by his father's defeat in 1992. Then, the Democrats' main message had been: "It's the economy, stupid."

Determined to avoid his father's fate, the younger Bush intended to concentrate on the home base. Al Qaida had other plans for him. David Cameron, too, has huge domestic concerns but he has never believed that a wise British government can retreat to the island fastness.

Foreign affairs have a further advantage: they are fun. This does not only apply to meetings in the White House. Since becoming PM, Cameron has relished the chance to head the new National Security Council, with its preliminary papers and the wide-ranging discussions.

In dealing with foreign affairs, Cameron has one great asset. He has no illusions, and approaches the big questions as a Tory, not an ideologue. Michael Gove is a neo-conservative, and Liam Fox, William Hague and George Osborne have all been attracted towards neo-con positions.

Cameron, by contrast, has never believed that democracy is an infallible political antibiotic, and that as soon as you open the tailgate of the jeep to scatter candies for the kids and votes for the parents, everyone will be cheering. Yes, he would probably have taken Britain to war in both Afghanistan and Iraq. But he would have asked many more questions than Tony Blair did (as would Margaret Thatcher). Before going in, he would have insisted on knowing how Britain would get out. He would always have wanted to hear the worst-case analysis. In that respect, he is a neo-Kissingerian.

Political realist

Henry Kissinger dealt with the world as it was, not as he would have liked it to be. To him, the aim of foreign policy was the defence of the national interest. But this was rarely a simple matter of unilateral action: it usually involved a complex blend of hard power and soft power, of American assertiveness and co-operation with allies. In 1066 and All That, we learn that there can be no solution to the Irish question, because as soon as somebody finds one, the Irish change the question. Dr Kissinger would agree that the big questions often require temporary expedients, because permanent solutions are impossible.

While sharing that cast of mind, Cameron is more of an idealist, as befits someone of his relative youth. It is those in the sere and yellow leaf of elder statesmanship who are inclined to murmur: "After such knowledge, what forgiveness?" That is not the PM's style, as was evident in his handling of the Megrahi affair. There was a cynical case for condemning the release, as he did. The decision was taken under the previous lot, in an underhand fashion. So there were good grounds for Cameron to say what he did, and land the opprobrium squarely on his predecessors.

Cameron has another asset: he finds it easy to strike up a rapport with foreign leaders. He has always got on with Barack Obama, and he copes as well as anyone does with Nicolas Sarkozy's volatility. Angela Merkel and he have had differences on Europe, which left her exasperated and threatening non-cooperation. As she has come to recognise, that is not realistic. From the British point of view, it is also useful that those other three leaders all face electoral adversity. None of them is able to patronise the new arrival from a position of impregnable assurance.

That said, David Cameron does not confuse easy personal relations with enduring diplomatic success. He knows that the British have always made much of living on the high seas. No Little Englander, he does not want to be a Little European either. This explains the upcoming visit to India.

The previous government ignored the Foreign Office's resources and brushed aside its advice. That did not advance British interests. Cameron has already come to admire the diplomats with whom he has had dealings. That should lead him to respect the system, and the ethos which produced them. Diplomats tend to be wary, and wariness is a wise prejudice in a dangerous world. Even amid the splendour of foreign capitals, Cameron would do well to beware the treachery of the unexpected.