IT is summit season again. In just over a week we have had three. The Nato summit was held in President Obama's home town Chicago; the G8 met in a display of conspicuous parsimony at Camp David rather than in the usual grand resort; and yet another EU summit took place in Brussels.

Summits happen so often now that leaders see more of their foreign colleagues than they do of their cabinet colleagues or even their families. Prime ministerial and presidential entourages criss-cross the skies in their planes. Aides scurry in the wake of world leaders, clutching bulging piles of agenda papers.

Of course, summits have existed as long as leaders have. Think of Henry VIII's Field of the Cloth of Gold, the Congress of Vienna or Yalta. Those were once-in-a-lifetime events that took leaders weeks or months to get to. But in the 1970s a new sort of summitry began, fuelled by easy air travel and an increasing role for leaders in foreign policy, at the expense of diplomats.

The argument for summits is that it is important to build personal trust between leaders so they can do deals with each other. The UK's former foreign secretary David Miliband argues: “If you've got a personal relationship with someone, if you've been able to show that you've respected them, helped them, they'll look to cut you some slack.”

But actually putting leaders together doesn't always make things better. Charles Powell, Margaret Thatcher's foreign policy adviser, says that she hated summits, mainly because they were attended by foreigners. “They also spent a lot of time reaching compromises which she hated, or a form of words instead of substance, which she also hated. So really she was not a happy bunny at summits in any way. The only way she found to make them work for her was to be ‘battling Maggie takes on all comers'. She was asked: ‘What does it feel like to be isolated one against 11?’ to which she replied: ‘Sorry for the 11.'”

Sometimes close proximity can lead to extraordinary personal rudeness. I remember President Chirac saying after a particularly dull intervention by a Finnish foreign minister at the Nice European summit, which he was chairing, that sometimes people miss a very good opportunity to shut up. He excelled himself at a later summit to discuss the siting of the European Food agency. When the Finns proposed Helsinki he caused great offence by asking: “Why would anybody want to put a food agency where people eat reindeer?”

Once leaders go into the summit room, the TV cameras are thrown out and the doors close, they are on their own. The staff, left hanging around outside, desperately try to find out what is going on in the meeting. Ulli Wilhelm, Angela Merkel's former spokesman, told me that the German chancellor had to resort to texting him with the latest developments inside the room so he could brief the German press.

The underlying concept of a summit is that it is easier to get agreement on difficult issues if you put leaders in a room by themselves rather than allow officials to interfere. That often means you are asking them to negotiate on very detailed texts that they don't understand. The former British prime minister John Major had to resort to desperate measures in his negotiations at Maastricht. Officials are allowed to enter the room to deliver messages but must then leave. John Kerr, Major's key European adviser, kept coming in and out of the room during the crucial endgame of the negotiations until Major got fed up and insisted he stay. Kerr had to crouch down under the table and whisper advice to Major as the last arcane points were agreed. That was fine as long as the chair, Prime Minister Ruud Lubbers of the Netherlands, put the amendments in French, German or English. But when he put them in Dutch, Kerr was flummoxed. Major would ask him what he thought of a particular proposal and Kerr would reply that he didn't know since Lubbers was speaking Dutch. Major would look down at Kerr in astonishment. He had understood perfectly since he was hearing the proposals in English through his headphones.

The number of people at summits has grown exponentially. European summits started with six delegates but there are now 27. If they all insist on speaking, and they feel they have to in order to justify their presence, then the whole day is gone in speeches. It certainly makes it impossible to do deals round the table. The key parties have to withdraw to negotiate in private. That can leave those excluded feeling increasingly testy.

By arrangement with the Guardian