The National Farmers' Union last week kicked off its latest attempt to highlight low milk prices.

It has challenged dairy farmers to stand up and be counted by submitting an invoice to the NFU for the difference between farmgate milk prices and production costs.

The move follows a recent survey by the union, which indicated that average ­farm costs have risen by 0.78ppl over the summer because of higher energy and feed prices.

Thousands of invoices have been distributed to dairy members.

Agricultural consultant Gwyn Jones said: "It is time to enable milk producers to pass on their extra costs in the same way as other people in the supply chain pass on their costs to milk producers."

But milk buyers at processors and multiples need not fear a flood of invoices arriving in the post after the the union backed away from urging farmers to submit them to dairy companies. Indeed, it has not yet decided what it will do with the bills, beyond totting up the shortfall experienced by its members.

But Jones said the popularity of the campaign could also turn out to be an important indicator of farmers' appetite for taking collective action in order to improve their bottom lines.

In recent months, they have been criticised by industry leaders for their lackadaisical response to requests for action and campaigns that are designed to help them.

Jones added: "I appeal to dairy farmers throughout England and Wales to support this campaign.

"It has the potential to make a real impact for the better on the industry. But improvements will only come if we get a huge response", he said

"In the short term, a substantial price increase across the board is desperately needed in order to stop the dairy industry bleeding to death."