But in a ruling today, the Advertising Standards Authority supports the view of the British pig industry that pictures of outdoor pigs don't indicate that all Red Tractor pigs are free-range, especially as the industry is careful to use images of indoor pigs as well.

The advert that aroused the ire of Compassion in World Farming and Animal Rights UK showed Jimmy Doherty on his own farm. Red Tractor critics claimed this could mislead shoppers into believing that all Red Tractor pork came from free-range pigs.

But BPEX told the Advertising Standards Authority it was disappointed by these complaints as it been careful to ensure the advert was representative of farms in the Red Tractor scheme.

It argued that it was not unreasonable to show Doherty on his own farm, particularly as the film also showed footage of indoor pigs.

In dismissing the complaints by Compassion in World Farming and 86 others, the Advertising Standards Authority said it accepted the aim of the Red Tractor scheme was to ensure pigs were raised to good standards.

"We considered that viewers would understand that the farm shown was Mr Doherty's and featured in the ad because he was, for the purposes of the ad, a representative of the scheme," says the Advertising Standards Authority.

"We considered that viewers were unlikely to believe that all the farms in the scheme would necessarily be comparable to his or that it represented all the farms in the scheme, only that Red Tractor pigs were 'raised to good standards by responsible farmers'."

NPA chairman Richard Longthorp said today, "I am disappointed that, despite efforts by the industry and a personal commitment from me to work closely with Compassion in World Farming on areas that should be of common interest, they continue to wage this war of attrition against us.

"I fear in reality they may be more interested in self-promotion than in genuine promotion of animal welfare in farmed animals across the world."

BPEX head of marketing Kirsty Walker said, "We went to great lengths to make sure the campaign as a whole gave a true and accurate picture of the British industry. We are pleased the Advertising Standards Authority has agreed with us and rejected these complaints."

Some of the complaints to the Advertising Standards Authority were the result of an anti-Red Tractor crusade by animal rights campaigners on Facebook, provoked by last year's Harling Farm disclosures. The Harling Farm episode resulted in a farmer committing suicide and an employee being sent to prison.

In its ruling today the Advertising Standards Authority says it notes, from the complaints received, that this particular farm had fallen below Red Tractor standards.

But the Agriculture and Horticulture Development Board had explained that the farm had been removed from the scheme and a number of changes had been made to Red Tractor standards, and more stringent inspections introduced.

"We considered that the monitoring of such schemes could not be absolutely infallible and one incident did not undermine the legitimacy of the Red Tractor scheme," said the Advertising Standards Authority.

In response to today's ruling, NPA chairman Richard Longthorp stressed the animal welfare credentials now underpinning the Red Tractor scheme which covers over 90 per cent of slaughter pigs in Britain. These include the introduction of quarterly Real Welfare audits by vets.

"Real Welfare is a high-welfare system, researched and tested by university scientists over several years, for monitoring pig welfare," he said.

"By measuring iceberg indicators — including tails, bodies, legs and hospital care — Real Welfare removes subjective judgements on animal welfare. Brussels considers this to be the most effective way forward in improving animal welfare, but other countries are nowhere near as far forward with it as the British pig industry."

A similar scheme, AssureWel, which is underpinned by the same science, is now part of RSPCA's Freedom Food standards. "As a society we must always look after our farmed animals compassionately and responsibly and that's why we are now collecting scientifically robust data on the welfare of our pig units," said Richard Longthorp, who is a member of both schemes.

"Compassion in World Farming and Animals Rights UK should be careful what they wish for. If they continue in their attempts to undermine Red Tractor standards, there is a danger they will drive customers into the arms of less welfare-conscious producers in other countries.

"Red Tractor members are inspected to ensure the pork they produce comes from pigs that are well looked after and raised to good standards by responsible farmers. The Advertising Standards Authority acknowledges as much in today's ruling, and it would be a step forward for animal welfare in this country if animal welfare and animal rights groups supported our goals."