Speaking at the NFU Conference in Birmingham, NFU president Meurig Raymond said that too often changes are made to supply contacts at short notice.

“It us scandalous that farmers are so often the last to know, and the first to pay, when this happens.”

He said that the adjudicator had been given powers to oversee first the voluntary code and then the statutory code as well as the power to fine.

“It has been a long journey, but now Christine Tacon has shown her mettle with a devastating report on Tesco’s conduct.

“This isn’t the end of the road.”

Mr Raymond added: “The code must be extended across the supply chain and the adjudicator should oversee other voluntary codes, like the ones on dairy contracts and red meat specification.”

Mr Raymond also called on the government to ensure that farmers across the country receive payments from the Basic Payments Scheme immediately.

He said there had been an unacceptable delivery of the scheme in England and Wales that has seen almost a quarter of farmers having received no payments by the end of January.

“In this market, thousands of farm businesses and those supplying farmers rely on the BPS to help pay their bills, their rents and their mortgages,” the NFU president said.

“In England today around 16,000 farms have still not had their payment.”

The Environment secretary Liz Truss told the conference that it was vital that the government carried out its calculations accurately as it could face huge fines from the European Commission.

She said the fines, or disallowance, were already running to £70 million a year.

“Money we should be investing to improve the growth prospects of British food and farming,” the environment secretary said.

Mrs Truss added that the Rural Payments Agency has entered and checked 80,000 claims and had now paid out more than £1 billion to 71,000 farmers – 81.5 per cent of those eligible.

She said the government was on course to make almost all the payments by the end of March

“For farmers who have not been paid, we will continue to work with banks so they are able to access finance,” she promised.

She added that some farmers had been able to access advance payments through a hardship fund and there had also been exceptional payments for those farmers facing difficulties, including a one off support of £26.2 million for the dairy sector.

Mrs Truss said that now the data has been entered onto the system, next year’s payments should be simpler.