The protest took place at the Robert Wiseman headquarters

During the second blockade in a fortnight, farmers targeted eight sites as part of the campaign for a fairer price for their milk.

According to the National Farmers Union (NFU), one in four Scottish dairy farmers have gone out of business over the last six years.

However, milk processors have insisted they pay top prices.

John Kinnaird, president of NFU Scotland, said: "There are only 1,400 dairy farmers left in Scotland and the industry is now at breaking point."

These family farms represented at protests today are being run out of business John Kinnaird NFU Scotland

There were almost 5,000 producers about 20 years ago.

Ken Boyns, head of economics at the Milk Development Council, said the UK retail average price for milk was about 52p a litre.

In 2003 it was estimated that supermarkets made about 13p a litre, processors about 16p a litre and farmers 18p a litre.

In 2004 the average UK milk price received by the farmer was 18.5p but Mr Boyns pointed out that production costs vary across the country.

While supermarkets, corner stores and those delivering milk to the doorsteps have increased the price of milk, most dairy farmers have seen very little of it, the NFU said.

Mr Kinnaird added: "These family farms represented at protests today are being run out of business by companies that see no further than their next shareholder statement."

However, a spokesman for Wiseman Dairies, which was targeted in the protests, said it paid its farmers 20.1p a litre.

If farmers are forced out of business we may have to import milk and the price is likely to increase Graeme Millar Scottish Consumer Council

"That is a long way from the 17p being quoted by farmers taking part in the protests," he said.

"Our profit is 2p per litre with our figures for the last financial year showing 5% profit, which is by no means excessive."

The Scottish Consumer Council gave its backing to the farmers and called for discussions between all those involved.

Its chairman, Graeme Millar, said: "Many consumers are likely to be surprised to find that only around a third of what they pay for milk goes back to the farms that produce it.

"Farmers deserve a better deal and milk processors should get together with retailers and the farmers to decide how this should best be done - without passing on any increased cost to consumers.

"It is in the interests of consumers that the marketplace works. If farmers are forced out of business we may have to import milk and the price is likely to increase. No-one wants to see that happen."

Dr Kevin Hawkins, of the British Retail Consortium, said farmers supply dairies not supermarkets and it is processors and smaller retailers who get money from price increases.

We have too much milk, too many farmers producing too much milk Sean Rickard Economist

Scottish Green Party co-convener, Robin Harper, said: "It is sad that the situation has come to this - but it is time to stand up for what is right and to demand fair trade for farmers.

"The continuing exploitation of dairy farmers by Tesco, Asda, Morrisons and Sainsbury's, and the milk processors is unacceptable. Processors cannot avoid responsibility."

The Greens have called for a supermarket regulator to police the industry.

The Scottish Tories' agriculture spokesman, Alex Fergusson, said: "Scottish Conservatives believe that the time has come to strengthen the existing Supermarket Code of Practice to give it real teeth, if necessary by new legislation."

The Scottish Socialist Party supported the farmers' "direct action".

MSP Rosemary Byrne said: "Dairy farmers deserve a fair price for their product - instead, they're being squeezed by the vice-like grip of agri-business and the supermarket chains."

Farmers want a greater share from milk processors

Sean Rickard from Cranfield University used to be the chief economist for the NFU.

Mr Rickard said: "We have too much milk, too many farmers producing too much milk, it's basically a commodity and as long as you're in that position the price will always be weak."

He said farmers should join together into co-operatives to process milk if they want a greater share of profits.

Dairy farmer John Cummings was taking part in a protest outside Robert Wiseman headquarters in East Kilbride.

He insisted there was a shortage of milk in the UK this year.

He added: "The housewife is paying in the region of 55p and the farmer is getting 17p.