Hundreds of angry pig farmers have been protesting in London to voice their desperation at the crisis facing their industry.

The National Farmers' Union and the British Pig Association backed the march to urge shoppers to buy British pork rather than foreign imports.

British pig producers say the crisis in agriculture and the additional costs of banning the stall and tether system of production for more welfare-friendly pig units has hit them hard.

The strength of the pound and overproduction of pork worldwide have added to the problems, pushing prices to new lows.

Nearly 2,000 people set off from Temple to Trafalgar Square

They are calling on Prime Minister Tony Blair to put an end to "Cruel Britannia" and order his ministries to put a ban on buying pig meat from foreign farms which would be illegal in Britain.

Marchers walked to Trafalgar Square where the Reverend Gordon Gatward, the agricultural chaplain for the county of Lincolnshire, called for a minute's silence as a mark of respect for those who have lost their livelihoods during the crisis.

Protesters then made their way to Downing Street to deliver a letter to Mr Blair.

"Farmers are proud to deliver this high standard and trust the consumer will enjoy eating our pig meat and chose to eat British every time," said an NFU spokesman.

British Pig Association Chairman John Godfrey, a pig farmer from Lincolnshire, said: "These are desperate times for the UK pig industry. Our survival is at stake as we face crippling losses which look set to continue well into the year.

"British pork, bacon and ham meets the most exacting demands for animal welfare, quality and traceability. We believe the consumer should be made aware of this superiority when making their purchases."

Pig farmer Bernard Howard said there were also fears that pork from elsewhere in Europe could lead to a scare similar to the BSE beef crisis.

He called on Mr Blair to "restict the feeding of herds in France, Holland and Belgium on meat and bonemal. If you remember meat and bonemeal was the main cause of the BSE disease".