Farmers and food producers stand to lose almost ￡300m from the trade deal with Australia and need government help, a report by MPs says.

       Boris Johnson vowed to “protect” the sectors when seeking his first post-Brexit agreement – but then overruled other cabinet ministers to strike a deal that effectively removes import tariffs immediately.

       Trade experts have concluded the agreement hands Australia an export boost six times greater than the UK’s likely gain, estimated to be just 0.08 per cent of GDP by 2035.

       Now the Commons environment committee has seized on a government admission that the puny benefits will partly come from “a reallocation of resources” towards manufacturing.

       The estimated losses for agriculture, forestry and fishing (￡94m) and semi-processed foods (￡225m) – with small gains for other food, drink and tobacco products – add up to an overall deficit of ￡278m.

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       Robert Goodwill, the committee’s Conservative chair, said ministers must “ensure the sector is no worse off” from the Australia agreement.

       “The government must commit to helping the food and farming sector win back the ￡278m worth of lost growth it will experience because of this deal,” he said.

       He noted a “plan to appoint new trade envoys to push our exports”, adding: “We will be watching the numbers and holding the government to account.”

       The call comes amid fresh attacks on the government for pushing ahead with implementing the deal before it has been fully scrutinised by a different committee.

       It was formerly laid before parliament on Wednesday, triggering a 21-day day period – under the Constitutional Reform and Governance Act (CRaG) process – before it can come into force.

       Angus MacNeil, chair of the international trade Committee, accused the trade secretary Anne-Marie Trevelyan of breaking an “explicit commitment” made to the Commons.

       “To so frivolously break this promise sets a dangerous precedent for future agreements and demonstrates how little this government respects parliament,” he said.

       The environment committee report also echoes criticism by Henry Dimbleby, a food adviser, that the approach to new trade deals risk “exporting cruelty and carbon emissions abroad”.

       The Independent revealed that meat from cows transported for up to 48 hours without rest – conditions banned in the UK – can now be imported from Australia.

       It is “unlikely that much food” failing to meet core standards will enter the UK as a result of the Australia agreement, the report says – but that might not hold true in future deals.

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       Ministers should commit to those standards – on deforestation and outlawing chlorine-washed chicken and the use of hormone growth chemicals in meat, for example – ahead of negotiations taking place.

       “We want our high UK animal welfare and environmental standards baked into every trade deal we do from now on,” Mr Goodwill added.