Hywel Williams MP has called for a halt to diving at the site

Police and ambulance crews attended the scene when Mr Amison was reported to be in trouble in the pool, which is 108m at its deepest point.

Three other divers have died at the quarry in the last three months, prompting calls for increased safety measures.

North Wales Police were unable to say on Sunday whether Mr Amison had been diving alone or as part of a group.

It was also unclear if he had been free-diving or had been using aqualungs.

'Catalogue of deaths'

In December 2001, Mick Gott from Derbyshire and Jason Barrass from Preston died in separate accidents at the Dorothea quarry within 48 hours of each other.

Another diver had died at the site in the previous month.

The fatalities prompted calls from Caernarfon MP Hywel Williams for a halt to diving at the site.

Divers have been urged to stay away from the quarry

"We just can't allow this catalogue of deaths to continue," he said in December.

"Sometimes regulations are necessary to protect people from endangering their own lives in such a terrible fashion."

The quarry is privately owned and divers using the site have been warned that they are trespassing.

In the past its owners have tried to block access to the pool with little success.

They have urged diving enthusiasts to stay away until they develop a formal diving centre and first aid facilities.

Diving experts say the quarry is steep-sided and gets very cold, which can lead to accidents including breathing equipment freezing up.