Thousands of salmon were poached alive when a lice treatment process at Scottish fish farms went disastrously wrong, it has emerged.

More than 175,000 salmon died when the water they were swimming in was overheated, prompting calls for those responsible to be prosecuted for cruelty.

The catastrophic mistake by staff at farms run by the Norwegian multinational, Marine Harvest, cost millions of pounds and led to over 600 tonnes of dead salmon having to be incinerated.

The deaths were largely responsible for a 16 per cent drop in the company’s Scottish salmon production and there are now fears it may lead to price rises for consumers in the run up to Christmas.