BBC Correspondent Roger Harrabin describes the mishap on BBC Radio 4's Today programme

Mr Prescott, who is also the environment secretary, was taking part in a dive designed to highlight the destruction of coral reefs in the Indian Ocean when his face mask filled up with water.

But the deputy prime minister, an experienced diver, remained calm, cleared his mask and continued with the dive.

Conservation grant

Mr Prescott later announced a �300,000 grant for coral conservation in the South Asian region.

He said: "Too many people still think that climate change is only a theoretical problem.

"In small island states like the Maldives people know it is real.

Nearly 90% of the reef has already been wiped out

"Coral reef damage that I have been shown here is a clear indication of the link between climate, oceans and land based pollution."

The deputy prime minister added: "Coral reefs are the miners' canaries of the oceans. The world needs to take notice."

Badly-fitting mask

Earlier, Mr Prescott had his own scare in the water around the coral reefs.

Describing the deputy prime minister's dive, BBC reporter Roger Harrabin, said: "While we were underwater a rather over-zealous helper thought he would aid us with a photo-opportunity.

"About 30 feet under the water, he jammed me up against Mr Prescott to get a photograph of a giant fan, an under water fan, which was waving.

"Mr Prescott and I thought the fan was fragile, both of us backed off it because we didn't want to damage it.

Mr Prescott is an experienced diver

"I think Mr Prescott possibly got knocked in the process, his mask completely filled up with water. It seemed to affect his buoyancy."

Mr Prescott remained calm throughout the ordeal and was more concerned about seeing the state of the coral.

"He cleared his mask. He continued to have problems through the dive because it was a badly-fitting mask he had had to borrow and he had a few problems," the BBC reporter said.

The UK minister's dive was intended to highlight the destruction of the area's coral reefs. Up to 90% of the coral in the Maldives is believed to have died.

The El Ni�o current is thought to be responsible for some of the deterioration in the coral. Global warming is also believed to be a major factor.

Mr Prescott will use his first-hand experience of the problems faced by coral to take to international negotiations on the state of the oceans and global warming.