The Tories are calling for the Farming Minister to resign after delays to a new subsidy system for English farmers.
The NFU passed a vote of no confidence in the RPA
Shadow agriculture minister James Paice said the minister, Lord Bach, had lost the confidence of farmers.
He said, in the House of Commons, there had been a "catalogue of incompetence and ministerial denial" over problems at the Rural Payments Agency.
Environment Secretary Margaret Beckett spoke of her "deep regret" at delays but rejected charges of complacency.
The new system works out what subsidy each farm should get according to past receipts and their land area.
Ministers had promised the bulk of the new payments would be paid by the end of the month.
Johnston McNeill, the RPA's chief executive, was replaced by Mark Addison, a former acting permanent secretary in the Department for the Environment, Food and Rural Affairs (DEFRA), after the agency admitted that target was unlikely to be met.
Mr Paice, raising an emergency question in the Commons, said Lord Bach should have seen this coming and prevented it from happening.
"The government's usual 'blame somebody else' line will not wash," he said.
"Lord Bach criticised others for saying what was abundantly clear to everybody else - he was wrong.
"He has lost all credibility in the industry for which he's responsible and should go. This House, and more importantly, the farming industry, deserves better."
Mrs Beckett said she understood and shared "the anxieties that these events will cause to the farming community and deeply regret that this unacceptable situation has arisen".
She said she had been told for the first time on 14 March that it would no longer be possible for the RPA to make the bulk of the payments by 31 March.
There were "substantial problems" facing the agency in getting payments to farmers, which were "much greater than had previously been reported to ministers".
The RPA was now focusing on getting the payments out to farmers "as fast as legally possible", she said.
She could not give a specific date for the payments, but defended Lord Bach, insisting he had maintained "the closest possible interest" in the situation.
Mr Paice said Mrs Beckett should be "embarrassed" and "ashamed" by a recent Defra newsletter report which claimed full payments were on track for farmers.
He urged her to consider making an interim payment for anyone who cannot receive the full amount by the end of March.
Mrs Beckett said she had been embarrassed by the article, but added that she would not rule out the potential for interim payments to farmers.
Chris Huhne, for the Lib Dems, claimed the introduction of the scheme had been botched in England.
He argued that ministers had to take their share of the blame, especially as payments in Scotland and Wales had virtually been completed.
Mrs Beckett said there had been a much smaller number of claimants in Scotland and Wales.