The UK's team for the World Summit on Sustainable Development has left for South Africa amid doubts about what they can achieve at the meeting.

Critics have questioned how the 60,000 delegates at the World Summit on Sustainable Development can make real progress on reducing poverty and protecting the environment.

Unless we are able to tackle some of these problems together, together we will destroy the planet

Margaret Beckett Environment Secretary

Prime Minister Tony Blair has also come under attack for spending only a day at the summit - something green campaigners say contrasts with his efforts at trade meetings.

Downing Street dismissed the criticism and on Friday Environment Secretary Margaret Beckett insisted the summit, which starts on Monday, could change how development issues were tackled.

Late arrival

Deputy Prime Minister John Prescott is leading the team, which includes Mrs Beckett, International Development Secretary Clare Short and Environment Minister Michael Meacher, who was reportedly left off the original list.

Mr Blair will join them for one day - 2 September - and will reportedly give a five-minute speech.

His alleged lack of interest in environmental issues has angered some green campaigners, but Downing Street said the logistics of speech times had yet to be decided.

60,000 delegates are going to Johannesburg

Mike Childs, from Friends of the Earth, said: "Even Tony Blair can't save the planet in five minutes.

"So much for the UK Government making a great priority of the Earth Summit.

"Before the last world trade ministerial meeting in Doha, Mr Blair flew around South America drumming up interest in freeing up trade for big business.

Even Tony Blair can't save the planet in five minutes.

Mike Childs Friends of the Earth

"In contrast, his five minute showing in Johannesburg looks like the bare minimum he can do to get a good headline without putting in too much diplomatic effort."

Busy week

The prime minister is accused of not putting words at last year's Labour conference about tackling poverty and global warming into action.

But a Downing Street spokeswoman told BBC News Online: "The prime minister will clearly be there towards the end, as well as all the other leaders.

"Most of the heads of governments are turning up for the last day or two. They have delegations working in the previous week."

Beckett: Cutting poverty is a key way of protecting the environment

The huge size of the summit has alarmed some campaigners, as has news that US President George Bush will apparently be on holiday rather than travelling to South Africa.

But Mrs Beckett insisted the summit was not a pointless exercise.

"The point is that this is a whole range of complex, inter-related issues which are crucial to the future of all of us," she told BBC Radio 4's Today programme.

"Nothing is more conducive to environmental degradation than world poverty," she said.

The summit comes as Greenpeace accused Tony Blair of hypocrisy over the Home Office's decision to install an air-conditioning system blamed for adding to global warming.

The department says the system, to be used at its new London headquarters, has been tested to get the best balance of value, safety and "environmental attributes".