David Cameron's government must intervene in the growing row over the price of milk, farming leaders have warned ahead of a summit on the growing controversy today.

Farmers unions from across the UK will hold crunch talks ahead of a meeting with supermarket giant Morrison's tomorrow.

Their members are angry at what they say are unsustainably low prices.

Protests were sparked when Arla, Britain's biggest milk co-operative, announced a price cut of 0.8p per litre, taking the standard litre price to 23.01p.

As part of a wave of action, farmers have cleared a number of supermarket shelves of milk, including in Ayr, in what is being called the Milk Trolley Challenge.

Some have also called for a consumer boycott of major supermarkets until dairy farmers are paid more for their work.

Farmers say that they need to receive at least 30p a litre to cover their costs, but the average price in June was just 23.66p.

A spokeswoman for the National Farmers Union (NFU) said that Conservative ministers had to intervene.

"This is a crisis. Farming leaders will be reiterating or call for a ministerial meeting," she said.

A spokesman for the Department for Environment, Food and Rural Affairs (Defra) said that ministers "maintain a regular dialogue with farming unions and industry."

"We look forward to discussing these issues with them further".

Last week Scottish Rural Affairs Secretary Richard Lochhead wrote to his ministerial counterparts across the UK calling for a summit on the issue.

He called for a joint approach to the chief executives of all major UK retailers and food services companies to ensure a fair price is paid for Scottish and UK produce would be welcomed.

In the latest protest yesterday two cows were herded through one supermarket's aisles.

The heifers were accompanied to the Stafford store by around 70 protesters - and the police.

One of the campaigners complained that milk in the shop was being sold more cheaply than water.

A spokesman for Staffordshire Police said: "Officers were in attendance to ensure that the protest remained peaceful and minimal disruption is caused to the general public."

Meanwhile, many consumers say that they would be happy to pay more for their breakfast pint, according to a new survey.

Normal supermarket prices range from 89p to £1 for four pints of milk.

But when more than 1,000 people were asked by market research company Mintel, just over half (51 per cent) said that they would be prepared to pay more than £1, with the average saying they would hand over £1.28.

Farmers fear that they are being squeezed in a price war between supermarkets.

Arla has said that high milk production across the world and low demand from China and Russia had had an impact on prices.

On Saturday, The Herald reported that Ayrshire farmer Bryce Cunningham, 28, has become involved in direct action because he is losing £200 a day.

He said: "I'm currently losing £200 every day. I'm trying to do everything I can to keep the business going.

"I can't provide money towards my wife who is on maternity leave.

"I'm finding it a struggle to do things."