The prince's office said greater use of green energy and fewer plane and car journeys helped Prince Charles cut his carbon footprint by 18 per cent to 2,795 tonnes.

For domestic travel, the prince's Jaguars, Audi and Range Rover now run entirely on biodiesel made from used cooking oil, and his 38-year-old Aston Martin is fuelled by bioethanol from surplus wine.

'I really do believe that the contribution their royal highnesses make to national life continues to develop and broaden,' said royal aide Michael Peat.

The Clarence House also said Charles and the Duchess of Cornwall had tried to cut costs 'at all levels' and their personal spending dropped by &pound400,000 to &pound2.2 million.

It said the prince and his family - including sons William and Harry - cost only four pence a year for every man, woman and child in the United Kingdom, the Daily Mail reported.

But Labour MP Ian Davidson, of the Public Accounts Committee, warned that his colleagues would continue to examine the Duchy's accounts 'with vigour'.

ASSOCIATED PRESS