Downing Street has been accused of reopening the door to imports of chlorinated chicken and hormone-treated beef, after a leaked memo instructed ministers to have “no specific policy” on animal welfare in US trade talks. The letter from No 10 states that the ministerial mandate for the US negotiations was “being updated to reflect” the fact that the UK was to have no policy position on animal welfare. The revelation will raise more concerns about the government’s commitment to upholding “high environmental protection, animal welfare and food standards”. The note, seen by the Observer and dispatched at the start of last month, gave approval for the US trade talks to go ahead and set out the conditions of engagement. It reveals serious cabinet unrest over the shape of a US deal and appears to suggest UK regulations could be changed to accommodate an agreement. It also makes clear that talks were to be used to “maximise leverage” in trade negotiations with the EU. “Consultation and agreement from relevant colleagues is sought before agreeing to change domestic policy or regulations as part of the negotiations,” it states. “In the context of preserving the integrity of UK domestic law, any decisions taken in sensitive areas … must take into account the potential legal implications for the UK and be agreed by the relevant ministers.” The memo reveals how contentious the US trade talks are regarded as being within the cabinet. Issues were raised by 11 cabinet ministers, including health secretary Matt Hancock, environment secretary George Eustice and Mark Spencer, the chief whip. “Written responses were received from the health secretary, foreign secretary, the chief whip, the business secretary, the environment secretary, the chancellor of the exchequer, the justice secretary, the defence secretary, the culture secretary, the Welsh secretary and the chancellor of the Duchy of Lancaster,” it states. “All other members of the committee were content.” The briefing also states that a cabinet committee would return to the animal welfare issue “in June to settle all outstanding agriculture issues”, suggesting an unresolved split. Meanwhile, it demands that “ministers receive regular progress reports of concurrent EU and US negotiations to help maximise leverage and allow policy tensions to be resolved as they emerge”. A government spokesperson said that it had been “very clear since the outset that we will not compromise on our high environmental protection, animal welfare and food standards”. Campaigners want legal guarantees on those standards to be enshrined in an agriculture bill currently being debated in parliament. The issue has already prompted a Tory rebellion in the Commons. It comes after reports last week that the government was proposing a “dual scheme” that would see higher tariffs on US foods with lower animal welfare standards. It is not clear whether higher tariffs would also be linked to environmental standards. Alistair Carmichael, the Lib Dem Brexit spokesperson, said: “People can now see that promises made by Johnson and Gove were worthless.” Luke Pollard, the shadow environment secretary, said: “It is unacceptable for the government to allow our high food standards to be compromised and our farmers undercut in any future trade deals. Attempts by ministers to use tariffs and tax rates to get around their manifesto commitment on food standards won’t wash.” Nick von Westenholz, director of EU exit and international trade for the National Farmers Union, said: “The government made a manifesto commitment not to compromise on our high environmental protection, animal welfare and food standards in trade negotiations, and this commitment is explicitly stated in the government’s specific objectives for the US negotiations. We would expect UK trade negotiators to be rigorous in upholding these commitments.” A government spokesman said: “We will always stand up for British farming and are determined to use trade negotiations to secure new opportunities for farmers. “Having left the EU, we will get to decide how we set and maintain our own laws, standards and regulations, upholding our food, environmental and animal welfare standards. Our food regulators will continue to provide independent advice to ensure that all food imports into the UK comply with those standards.”