The intervention will help to put the environment at the top of the political agenda ahead of the meeting of G20 leaders in London next month.

Senior sources have revealed that Gordon Brown's Government wants to make more use on the foreign stage of Prince Charles's experience, expertise and contacts, particularly on climate change. Government officials believe that the Prince's passion to protect the environment is hugely respected abroad and that he can play an increasing important role as he inevitably moves closer to becoming king.

In Thursday's speech, the Prince will warn that a failure to act in the next eight years will have catastrophic effects for the planet.

In the country that is home to the world's largest rainforest, Prince Charles will urge world unity to combat deforestation in the run-up to the UN conference on climate change in Copenhagen in December this year.

Royal aides have welcomed the opportunity for the Prince to expand his role on behalf of the Government. One senior official said: "It could be argued that he has already established a role as an international statesman, especially on green issues.