British cavers back above ground

John Hey's cave phones kept the six in contact with the outside world

The six British cavers trapped for more than a week in a cave system in Mexico have been rescued.

They've emerged from the flooded caverns to a diplomatic storm about whether their expedition had the right visas.

But one piece of kit which prevented their drama becoming a tragedy was a special radio - the Heyphone - which enabled them to transmit messages through the rock.

The radio, developed by a retired electrical engineer from Leeds, enabled the cavers' support team to guide the rescuers to the right spot.

We heard from the Heyphone's manufacturer, John Hey.

He explained how he lends out the equipment for a deposit of £300. Circuit diagrams are also available on the internet, for people who have the skills to build one themselves.

Heyphone: instructions and more information

Further details of the rescue from BBC News Online

The team of experienced cavers, some of them military staff, were rescued by UK specialist divers who flew to Mexico to provide help.

The rescue mission took most of Thursday, as each man was escorted through the flood waters using scuba diving equipment.

They had been waiting at an underground camp set up for just such an emergency.

None had suffered any injuries and had supplies of food and other equipment to keep them comfortable, plus communication equipment to keep in touch with their colleagues outside the cave.

We're feeling quite cheerful Toby Hamnett Rescued caver

The BBC correspondent at the scene, Claire Marshall, said the men told her they were "looking forward to a good beer".

They were fed hot tortillas en route to a military hospital in Puebla for check-ups, and are expected to travel to Mexico City on Friday.

As they emerged into the humid vegetation and a media scrum, one of them said they were never in danger and would have preferred to wait for the water to subside.

"The thing is, everything went as planned," Jonathan Sims said.

The men were well and jovial when they emerged from the caves

"We thought we might have a problem with the (water) so we put in a plan, we had food in there, communications," he said.

"The unfortunate thing is we got too much media attention."

The cavers appeared tired, but jovial as they asked waiting journalists and rescue workers if anybody had brought beer.

"We're feeling quite cheerful," said rescued caver Toby Hamnett.

Two British divers, assisted by Mexican underwater specialists, had entered the cave on Thursday.

One stayed with the men to instruct them on how to use the scuba equipment, while the other swam through the water with them one by one.

They had spent part of the time awaiting rescuers by playing games with a deck of cards fashioned from a logbook.

Their stay was legal as tourists, but there are indications that their activities were not of this type Armando Salinas Mexico's assistant interior secretary

The men's presence had sparked a diplomatic incident about their status.

Mexican President Vicente Fox on Wednesday asked the UK to explain what the soldiers had been doing in the Cuetzalan caves.

Mexico's assistant interior secretary Armando Salinas said the men "will be placed in the custody of immigration authorities" after their check-ups.

"We have reason to suppose that their actions could touch on our immigration law," he said.

"Their stay was legal as tourists, but there are indications that their activities were not of this type."

The British Ministry of Defence dismissed concerns, saying it was a sporting, not a military, trip.

The six men on the expedition, named Cuetzalan Tiger, were part of a 13-strong group from the Combined Services Caving Association.

The expedition was due to last 36 hours but the group got stuck after heavy rains raised the water level in the cave.

The men declined local offers of rescue, instead preferring to wait for two specialist British divers who flew to Mexico to escort them out.

Our correspondent said reports of resentment of the spurning of local offers of help had been "blown out of proportion".

As the diplomatic spat continued, a spokeswoman at Mexico's embassy said the ambassador met British Foreign Office officials, but she did not disclose details.