Mr Yonge claimed there was no alternative to the complete cull plans detailed by the government to stop the parasite which has already devastated salmon stocks in Norwegian rivers.

"It can hook a ride on other species of fish - it doesn't affect them, it doesn't kill them or give them the disease," he said.

"If you are trying to get rid of it in a river system what you have to do is kill all the fish in the river system.

"It is the only way of getting rid of them."

He said that meant everyone using the River Tweed in southern Scotland and the north of England had to be on their guard.

"Of course we don't ever want that to happen on the Tweed," he said.

"What we have to be intent on is never letting it get here in the first place."

He said it was important that equipment used abroad such as canoes, fishing rods or reels was thoroughly dried before being used on the Tweed.

The Scottish Government's plan would only be used if an outbreak could not be contained.

A special poison would be released to kill the parasites and their hosts.

It is hoped parasite-free fish would then repopulate affected rivers.