It started off as an SOS to save a remote island sanctuary for sea birds from the ravages of a flotilla of shipwrecked Spanish rats.

Two rat-catchers were scrambled on to the isolated Scottish isle with orders to trap every last rat that had managed to sneak ashore from the sinking fishing boat.

But yesterday as the pair were bedding down for their eighth night on the Atlantic outcrop, it became clear that the only creatures trapped on the island were the catchers themselves. During the course of a long, wet week of laying bait and traps, not a single rodent had been spotted, let along trapped.

The fears were raised a week ago when the Spinning Dale foundered on rocks at St Kilda, a remote archipelago 100 miles (160km) from the mainland. Conservationists feared that rats could swim ashore and devastate the huge population of ground-nesting birds on the double World Heritage Site.

Michael Russell, Scotland’s Environment Minister, expressed “great concern” at the risk to the islands, which until the 1930s had a human population that starved while no one of the mainland paid a blind bit of notice.

Rat-catchers were flown out by helicopter to make rat cakes, a mix of candlewax and chocolate, to see if they could catch any rats. None was found but the catchers themselves ended up embarrassingly trapped.

Abbie Patterson and John Sinclair, employees of the National Trust for Scotland (NTS), which owns the islands, were due to leave St Kilda yesterday but gales grounded the helicopter. With the fierce winds forecast to continue over the weekend the pair may be storm-bound until Tuesday.

The operation against the phantom menace was condemned as an overreaction by a local harbour master, who scoffed at the idea that fishing boats carried rats. Further embarrassment for the NTS came yesterday with an indignant statement by Bertie Armstrong, head of the Scottish Fishermen’s Federation, who also dismissed the idea that rats were found on trawlers. “For the Scottish fishing industry, nothing could be further from the truth and the last rats probably left the fleet with the demise of the steam drifters,” he said. “Rats simply don’t like clean diesel-powered fishing vessels and avoid them like the plague.”

No birds may have been harmed, and no rats recovered, but human casualties have mounted during the exercise.

A BBC news team aborted a boat trip to St Kilda after a cameraman broke his ankle and another fell sick from the crossing. Brian Ashman was taken to hospital after he fell on the way to Hirta, the biggest of the islands. His unnamed fellow cameraman was taken back to Harris to recover from his seasickness.

Susan Bain, who manages St Kilda for the NTS, said: “The weather is quite rough and we have had to forget about getting Abbie and John off. If we can’t get them off on Saturday we will have to leave it until Tuesday.”

The trust has defended the £2,000 cost of the operation, saying that if rats had got ashore and colonised St Kilda it would have cost £1 million to get rid of them. It said that it had a responsibility to investigate the risk posed by the wrecked boat.

“We could not take the risk of being 99 per cent sure there were no rats on St Kilda — we had to be 100 per cent certain. This is a site of international importance,” Ms Bain said. So far the only creature that has eaten the wax and cocoa bait set for the rats has been the famous St Kilda mouse, which apparently does not interfere with the birds’ nests.

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