TWO suspected IRA terrorists were being questioned last night after

they were arrested by armed police keeping watch on a hidden cache of

weapons and explosives.

Police said the store, containing 100lb of Semtex explosives,

detonators, and heavy automatic weapons, could have been intended for a

Christmas bombing campaign on the British mainland.

The two men, one said by police to have been carrying a loaded

pump-action shotgun, were challenged as they approached the spot where

the arms had been buried close to a coastal footpath in west Wales.

Police fired one shot during the confrontation, but no-one was

injured.

The men, both Irishmen aged 25-30, were taken under armed police

escort to Paddington Green police station in London where they were

detained under the Prevention of Terrorism Act.

Police had mounted a round-the-clock surveillance operation on the

cache for seven weeks, after a local man stumbled on it while out

walking his dog.

Villagers in nearby Newgale, population 120, were sworn to secrecy

about the find.

Chief Constable Ray White of Dyfed-Powys Police said the cache

contained enough explosives to make several bombs, adding: ''There was

enough kit for a terrorist unit to mount a sustained campaign.''

Commander George Churchill Coleman, head of Scotland Yard's

anti-terrorist branch, said: ''This could have been used for a Christmas

bombing campaign.''

Codenamed Operation Pebble, the surveillance was one of Britain's

biggest watch-and-wait exercises.

Officers lay concealed for seven weeks during some of the worst

weather ever experienced in west Wales.

Their wait came to an end on Thursday when two men arrived in

darkness.

A news blackout was imposed by press and broadcasting organisations at

the request of Scotland Yard.

Detectives believe the Semtex and guns were landed from a small boat

at night, to avoid the risk of detection at the ferry ports of Fishguard

and Pembroke Dock, which are under constant watch by Special Branch

officers.

Last night forensic experts were examining the haul, along with the

car said to have been used by the two suspects to travel to the arms

dump.

Police were also examining the possibility of a link with the shotgun

murders of Oxfordshire holidaymakers Peter and Gwenda Dixon, whose

bodies were found in undergrowth a few miles along the same path near

Little Haven in July. Their killer has never been caught.

Despite the latest explosives haul, police still fear the IRA could

use other caches to launch a Christmas campaign.

Commander Churchill-Coleman said the two detained men were not known

terrorists. They had not yet been identified.

''It is all speculation, but this could have been used for a Christmas

bombing campaign. We must still be vigilant and not complacent,'' he

said.

The cache was buried close to RAF Brawdy, a maritime search and rescue

centre, which is also close to a US Navy listening base. But police

would not speculate on any possible target.