The UN celebrates its 50th anniversary this year. For most of its first half century, says Parsons, whose career in the British foreign service never included a job that was not related to decolonisation, it focused primarily on dismantling the empires and settling the unending disputes and bloody civil wars they left in their wake.

But now the 'decolonisation machine' has done its work, not only is the landscape in the Middle East, the whole of Africa and much of Asia 'still littered with the debris of the last decolonisation', but the scene is now also dominated by a new one: the former Russian Empire.

In the guise of the Soviet Union, he says, the Russian empire 'masqueraded . . . successfully in the eyes of the Non-Aligned Movement as the anti-imperialist champion of national liberation for most of the life of the UN'.

Since its demise and the break-up of its old sphere of influence, a fresh wave of civil and separatist conflicts has surged.

As a result, the UN is doing much the same business in a much-changed world. With much the same rate of success.

Decision-making has accelerated, resolutions and peacekeeping mandates have multiplied as the superpowers' client states can no longer rely on Washington's or Moscow's uncritical support.

Yet UN interventions in the 1990s have proved little more effective than in the days when reaching agreement was like 'towing a recalcitrant brontosaurus through a glutinous swamp'.

Unless Security Council members have a strategic interest in intervention, there will be no decisive action to match the words.

Nevertheless, despite its inglorious history, the UN has not been a total failure. Its most important function - as a safety-valve - has too often been overlooked.

Resolutions came, went and were flouted by the warring sides in most conflicts.

But when the time came to back off, Parsons observes, they provided an 'internationally validated beacon on which both parties, once exhausted, could converge when it was politically impossible for either bilaterally to hoist the white flag'.

Over the years, the UN has had its successes. The Congo in the 1960s; more recently Namibia, Cambodia and Mozambique - although, as the subsequent history of the Congo and Cambodia has shown, nothing is forever.

However, the 50-year history of UN involvement in the Arab-Israeli dispute shows the international community at its worst.

Over the years, the General Assembly became so predictably one-sided (although arguably the Security Council was biased in the opposite, equally cynical direction), that the UN lost all credibility as a peacemaker.

Peace, where it has been made at all, has been made without UN intervention.

UN involvement in Somalia, Angola and the former Yugoslavia has been more recent. But it has been no more heroic.

Many more of Parson's themes deserve attention. There is the confusion of peacekeeping and peacemaking that blighted missions in Somalia and Bosnia and demonstrated that 'impartiality is incompatible with the use of force, which requires taking sides'.

There is the tendency of television to control the agenda and force the UN to involve itself in conflicts it would previously have avoided.

And then there is the rule that international outrage at unprovoked attack depends on the relative popularity and strategic importance of the aggressor and the victim.

Compare for example the UN's supine reaction to Iraq's 1980 attack on Iran and its reaction to Iraq's attack on Kuwait a decade later.

A further strand, perhaps of particular interest to students of East Asian and Chinese affairs, is the UN's long-standing insistence that the internal affairs of its member states, no matter how artificial their borders, are none of its affair.

This has been the excuse for ignoring civil wars and genocides worldwide, as it has been for China's suppression of Tibet.

'The most sacred of UN cows,' Parsons declares, 'has been the integrity of states within the existing frontiers . . . Separatism has been the devil incarnate.' But as the Soviet Union has broken up into newly-recognised states, Czechoslovakia has had its 'velvet divorce' and separatism has resulted in innumerable de facto but unrecognised statelets, he asks how much longer the UN will be able to resist the trend 'and insist on withholding recognition, except when it is agreed by all parties'.

As an old Foreign Office hand, Parsons occasionally shows his Britishness.

This is particularly so in the early years, when he does not even bother to conceal his youthful disgust at the ignominy of Britain's departure from Palestine.

There is also an undercurrent of resentment in his account of the UN as a body more concerned to make politically-correct attacks on Western imperialism than deal even-handedly in crises.

But later in his career, as his conversion to what he calls 'decolonisation man' is completed, his internationalism is admirable, if slightly bureaucratic.

His refusal to refer to later Secretaries-General by name is grating. It is as if the office could have been unaffected by their personalities.

But these are small quibbles. From the Cold War to Hot Peace is readable and informative, and its central theme of an organisation obsessed with decolonisation, but hamstrung by Security Council members' self-interested agendas in its attempts to broaden its scope, is cogently argued.

It is also, almost despite itself, a personal account. Without that personal touch, it would be less convincing.