Number 10 has defended John Prescott's two week round-the-world trip.

Speaking as the deputy prime minister arrived in Hanoi for the last leg of his 15 day tour, which has taken in the US, Australia and the Far East, Downing Street insisted it had been worthwhile.

Despite claims that Prescott effectively has no role in the government since the June reshuffle, a spokesman for the prime minister insisted he had an important part to play.

"The prime minister believes that the deputy prime minister is an extremely effective ambassador for the UK abroad," said the spokesman.

During his trip, Prescott has met with a series of leaders, and held a videophone discussion with the US vice-president Dick Cheney.

He kicked of the trip in New York, before heading for talks in Washington. After the US, he headed to New Zealand, going from there to Australia.

Prescott, who was travelling with four civil servants, then headed to Malaysia, before flying to Vietnam.

He returns from Hanoi, his final destination, on Tuesday.