MPs say better labelling of pork would help people make an informed choice
Two-thirds of imported pig meat could have been reared in conditions banned in the UK, according to a report by a cross-party group of MPs.
The high welfare standards imposed on British pork farmers since 1999 have left them at a "serious disadvantage" to overseas competitors, it added.
The committee also warned that British farmers did not get their "fair share" of the retail price of pork products.
The report comes ahead of a campaign by TV chef Jamie Oliver on pig welfare.
The EU plans to implement by 2013 a similar ban on the use of stalls and tethers as that imposed in the UK a decade ago.
Unlike their British rivals, farmers in countries like Denmark and the Netherlands will receive state support to make the changes.
But MPs on the Environment Food and Rural Affairs Committee found that currently up to 66% of imported pig meat could have been reared using these restrictive methods.
People were not being given a clear enough message about why they should pay a little more for British pork, they said.
The MPs' report warned: "The government must ensure that never again are UK farmers placed at such a disadvantage compared to their EU counterparts as a result of unilateral national action."
It added that confusing labelling meant processed foods containing imported pork could still be labelled as having been produced in the UK.
The report found that the UK pig herd had declined by 40% since 1997, to 470,000 breeding sows producing just over nine million pigs a year.
Over the same period, imports have increased to the point where half of the pork meat eaten in the UK comes from overseas.
The report said better welfare had imposed a "heavy financial burden" on the UK industry - estimated by Pig World magazine at £323m.
According to the British Pig Executive, most English pig farmers lose £7 on the sale of each animal, compared to the costs of rearing it - down from a peak of £25 in 2007.
Committee chairman Michael Jack said: "The English pig industry's adherence to high welfare standards has left it vulnerable to competition from European producers whose production methods do not match ours."
He said retailers and processors should deliver a fair price to producers, while the industry must take steps to reduce costs and increase productivity to secure its future.
Defra estimates the average commercial farm had losses of £4,100 in 2007-08.
Celebrity chef Oliver's new Channel 4 series, Jamie Saves Our Bacon, will encourage people to buy British pork on the back of the stricter welfare laws.
He claims the British pig industry is "on its knees" because so much pork is imported from EU countries.