Mr Blair's speech underlines the weakness of this summit

When a national leader at a global gathering takes the podium for his five minutes of speech time, he has a choice. He can use his precious allocation to make one or two memorable points with force, or he can try to cover the whole gamut of issues in bland banalities and let his presence stand as his main statement.

Unfortunately, Mr Blair chose the latter course when he addressed the Earth Summit in Johannesburg yesterday. "The issue for this summit," he said gravely, "is political will." Pollution, starvation, North-South interdependence, the achievements of Rio, the limitations of Rio, development (sustainable, of course) as a British government priority; Africa as a prime-ministerial passion...

Mr Blair promised more money for African development (up to £1bn a year – but not for another four years) and 50 per cent more for everyone else. He said that everyone should ratify the Kyoto protocol on climate change, while insisting that it was inadequate, and warned of "powerful, vested interests" in the way of the protocol.

Well, yes, that is all very true. But we knew all this before anyone went to Johannesburg. Agreement on the need to act is why most of the world's leaders are there this week and why the US President is not. The purpose of the Earth Summit was to set measurable timetables and targets, to show that the rich world was prepared to make changes, if not – if we are brutally honest – real sacrifices, to assist development in the poor.

Unwittingly, perhaps, Mr Blair simply underlined the chief weakness of this vast gathering: the size and diversity of interests that were bound to make comprehensive agreement elusive, and implementation still more so. And it did nothing to pre-empt President Robert Mugabe's predictable attack on Britain's colonial legacy. This, along with the prospect of US military action against Iraq, now threatens to fill the vacuum where, it was planned, serious, collaborative, discussion of long-term development issues should have been. Thus does another global gathering threaten to become mired in familiar North-South and East-West conflicts, rendering concerted action on development that much more difficult.