About 40 dairy farms close every week, according to Farm

They will be handing out leaflets outside the Tesco Extra Store at Lee Mill near Ivybridge on Saturday.

The demonstration, which is being repeated at other supermarkets across the country, has been organised by the pressure group Farm.

Tesco said it bought its milk from processors, not farmers, and could not dictate what farmers were paid.

We had to stop dairy production because of the appalling prices we received John Sherrell, farmer Are we seeing the end of fresh milk?

The aim of the demonstration is to persuade Tesco to come up with a better deal for farmers.

Shoppers will be encouraged to back their campaign by posting pre-written postcards calling for changes to be made and addressed to the chief executive of Tesco.

'Strong supporter

A Tesco spokeswoman said: "Tesco is British agriculture's number one customer and a strong supporter of the UK milk industry.

"Our aim is to work with our suppliers to create sustainable relationships with dairy farmers.

"We believe the most positive thing we can do is to continue to work with the supply chain to grow the amount of UK dairy products that we sell and develop new opportunities."

John Sherrell, 27, recently stopped dairy production at his farm near Newton Ferrers.

He said: "We had to stop dairy production because of the appalling prices we received - It was impossible to carry on."

Making a loss

A litre of milk costs about 50p in shops on average.

This year a parliamentary committee found that about 18p of every 50p was unaccounted for - lost in the supply chain.

Mr Sherrell said within a decade, his farm went from receiving 25p per litre to 16p.

On average, it had cost him about 22p to produce a litre of milk by the time he halted his dairy trade.

The farmer, who has continued with beef, arable and chicken farming, added: "We have a small, family-run farm and the dairy was our main focus for over 50 years.

"This pricing pressure has been going on for the last five years. By the time we ceased dairy production we were running at a loss."