Tony and Cherie Blair were entertaining Clare Short at dinner (which was in itself a noteworthy occasion, though it was not recorded at the time, because the pundits declared that the outspoken MP for Birmingham Ladywood was then deeply out of favour with the leadership). While they were talking, one of the Blairs' sons came downstairs in his pyjamas to say goodnight.
Coincidentally, the environment was mentioned, and the young Blair launched into a long and passionate green tirade, which concluded with a resounding statement: "That's what you politicians should be concerned about!" And so to bed.
His father admits that he was shaken. This was, he says, the first time the boy had shown an interest in anything political. But it helped start a process that could be instrumental in breaking a deadlock in international negotiations whose subject is nothing less than the future of the planet.
This Sunday an unprecedentedly powerful delegation consisting of the Prime Minister himself, the Deputy Prime Minister, John Prescott, the Foreign Secretary, Robin Cook, the Environment Minister Michael Meacher and Ms Short, now Secretary of State for International Development, arrives in New York for a summit of 70 or so world leaders. John Gummer, who was the Conservative secretary of state for the environment, is be taken along too, presumably for the sake of continuity. Their task is to examine progress since the Earth Summit five years ago in Rio de Janeiro.
Or rather, the lack of progress. For the draft declaration for this week's summit - it is written before the meeting begins - admits: "The state of the global environment has continued to deteriorate." It adds that "reversing the trend" is "more urgent now than ever" - but nations are further away than ever before on agreeing how this should be done.
The crisis presents the new Government's top people with their first opportunity to make a global impact; it is also the first important test of the "ethical", environmentally concerned foreign policy announced by Mr Cook as soon as he took office.
WHEN 108 heads of state and government met in Rio in 1992, it was said to be the greatest concentration of political power ever to have assembled in one place, but since then things have gone from bad to worse. These eminences signed a treaty to combat global warming, but emissions of carbon dioxide - the main cause of the climatic change - and concentrations of carbon dioxide in the atmosphere have reached new records. Despite another treaty to protect wildlife, at least 40,000 species have since become extinct. And, despite agreement on the principles designed to protect the world's forests, more than 100 million acres - an area five times the size of England - have since been cut down. All these trends continue to accelerate.
Worse still, the compact painstakingly agreed in Rio has broken down. This was struck between the rich industrial nations who are responsible for most of the damage to the planet so far, and the Third World whose development could complete the destruction. Understandably, Third World nations argue that they should be compensated if they now forego the cheap and dirty technologies used by industrialised countries to build their economies.
Under this deal, developed countries promised to start to change their ways, and also to increase aid to the Third World to enable it to develop more "sustainably". The side that reneged on the deal was the group of rich industrial nations.
All but of them will fail to meet their promise under the treaty to reduce emissions of carbon dioxide, returning them to 1990 levels by 2000. Far from increasing aid, the rich have cut it by $10bn, which is 20 per cent when measured as a proportion of their gross national product.
It is no surprise that the developing countries now reject the idea of new undertakings, and dilute existing ones - until the rich pay up. Negotiations preceding the summit, which have just ended in New York, have become bogged down. The present danger is that if the heads of state fail to reach agreement this week, the environmental crises will fall off theagenda; and they will not return to it until it is too late.
The high-powered powered British delegation - carrying with it the impact of freshness and authority that comes from a landslide election victory - probably offers the best chance of a breakthrough, if it measures up. Previously equivocal on green issues, the Prime Minister has shown more interest since his son's outburst. Shortly afterwards, he initiated a series of meetings with seven of Britain's leading environmentalists.
Two weeks ago he spent an hour talking about the summit with a larger group, led by Fiona Reynolds, head of the Council for the Protection of Rural England, who is a personal friend. The group included Sir Crispin Tickell, the former ambassador to the United Nations, and Derek Osborn, a former Department of Environment official who has been chairing the preparatory negotiations. Blair assured them: "The environment is the coming issue for this Government."
There have been signs recently that Downing Street has begun to understand the scale of the opportunity. After behaving as if the New York meeting was far less important that the EU summit in Amsterdam, or the G7 meeting in Denver, the Prime Minister's inner circle finally began to focus on it, and green issues have begun to move towards the top of the agenda. Last week officials were keen to stress that this Government was approaching the summit more positively by sending more senior ministers than the Conservatives would have done.
Global warming is a particularly contentious issue, and five proposals for controlling carbon dioxide emissions are on the table, ranging from a vague expression of intent - proposed by the United States - to demands for heavy cuts by small island states, whose passion is based on the fact that they may be erased from the map if sea levels rise as a result of climatic change. Britain, which is one of only two or three countries likely to meet its Rio commitments - an unexpected bonus after the collapse of the coal industry - has pledged a 20 per cent reduction in emissions by 2010.
Mr Cook has made global warming a priority, and Mr Blair is pressing for agreement on serious cuts in carbon dioxide emissions at the Denver summit. In New York the Prime Minister is expected to urge specific targets for tackling environmental damage and reducing poverty. Britain is also to push for a new initiative to rescue Africa, and will pledge to spend 50 per cent more of its existing aid budget on providing water - a major item on the New York agenda - education and health care in Africa.
That may not be enough to hold the pact together, however. Because of Labour's pre-election commitment to keep to Conservative spending targets, Blair can promise no more money for the next two years, though the Government is pledged to reverse Britain's decline in aid thereafter. There is little sign of other rich countries producing even as much as Britain, and the failure to come up with the cash promised at Rio remains a principal sticking point.
But there are few financial areas which could still make a difference. The poor countries are especially aggrieved at the West's failure to provide the aid they promised to help them implement a treaty on combating soil erosion, the subject of their central initiative at Rio. And now they are concerned to persuade the well-off to refund generously the Global Environmental Facility, a UN/World Bank fund which helps them buy clean technology. Specific pledges from Britain on both of these matters would have a disproportionate influence on the conference.
The most ingenious proposal is to be made by the European Union, which suggests a small tax on aircraft fuel to fund environmentally friendly projects. A levy of just a few per cent on the fuel in Europe alone could produce pounds 2bn a year for development. The EU could administer this revenue to evade ideological opposition in the US Congress to "global taxes".
Mr Blair is still putting the finishing touches to the speech he will make tomorrow in New York, knowing that if he fails to rise to the occasion, he may face sharper questioning across the floor of his home than across the floor of the House.