THE East Lancashire mother of one of the British cavers rescued from Mexico today said: "He's no spy."

Joyce Mitchell spoke of her relief after her six-day ordeal ended when son Chris became the first of the men to be pulled to safety.

She revealed that the real reason behind the expedition was to map a possible route between two cave systems.

But as she spoke, Mexican authorities announced that the rescued team could be kept in the country until after the weekend as police investigate claims they were looking for radioactive materials.

Last night, a police investigation was launched into whether the men, who had been on a military training mission, had in fact been searching for uranium, a claim denied by defence officials last night.

As the Foreign Office played down a rift with their Mexican counterparts, the country's president, Vicente Fox, said his government had demanded "clear information about what they were doing" only to receive answers which "frankly did not satisfy".

Joyce, who lives in Athol Street South, Burnley, with husband John, said: "It is a relief to know that Chris is safe, but we never really thought he was in any danger.

"He is very experienced and the team had plenty of food and equipment to keep them quite safely in the cave.

"They were quite prepared for something like this to happen and had taken everything they needed to last for longer than they planned to be down there. In fact, they left some food when they were pulled out.

"Chris spoke to his wife on Thursday night.

"Although we haven't been overly worried, it will be good to hear his voice.

"His wife tells me he seems absolutely fine and has been amazed by all the fuss.

"The confusion about the expedition has been very surprising.

"They were only in Mexico to try and see if there was a navigable route through a cave system between two mountains, that's all."

Chris, 40, a former St Theodore's pupil, now lives in Haverfordwest, Pembrokeshire, with his wife Tracey and two children.

He is a staff sergeant in the Royal Electrical and Mechanical Engineers and currently on a two-year posting training cadets.

Joyce said her son had joined the Army aged 21 and had never looked back.

She said: "Chris loves what he does and he has been involved in many expeditions with the Army during his time.

"He loves taking part in all sorts of sports and is a qualified PE instructor, climber, caver and diver.

"What has happened in Mexico certainly won't put him off doing things like this in the future. In fact he is coming back for a few days to see Tracey and the children and is then off on another expedition."

The cave diving group was made up of a scientist and members of the Combined Services Caving Association.

They had been in the cave system for four days when an exit tunnel flooded and blocked their way out. Seven other members of the team, organised with the Royal Geographic Society, had already made it out of the cave when the others became trapped.

A spokesman for the Ministry of Defence said they were hoping the team would be able to return to the UK over the weekend once they had been spoken to by the Mexican authorities about confusion over the visas used for the trip.