Animal welfare standards could be undermined if post-Brexit trade deals leave British farmers competing against less-regulated foreign rivals, peers have warned.
The Government's desire to secure trade deals after leaving the European Union could result in a "race to the bottom" on welfare as British producers are forced to cut costs, members of the the cross-party House of Lords EU committee said.
The intervention came as International Trade Secretary Liam Fox became involved in a controversy over whether chlorine-washed chickens would be allowed into the British market under any post-Brexit UK-US trade deal as he held economic talks in Washington.
As critics expressed fears that British food standards could suffer after Brexit, Dr Fox said any decision on such chickens would be "a detail" at the very end stage of negotiations.
The Lords' Energy and Environment sub-committee also raised concerns about the "overwhelming reliance" on EU citizens in crucial veterinary positions and urged ministers to make sure the industry was able to fill those roles after Brexit.
The report said: "Our evidence strongly suggests that the greatest threat to farm animal welfare standards post-Brexit would come from UK farmers competing against cheap, imported food from countries that produce to lower standards than the UK.
"Unless consumers are willing to pay for higher welfare products, UK farmers could become uncompetitive and welfare standards in the UK could come under pressure."
They warned that imports from lower-welfare countries could "undermine the sustainability of the industry or incentivise a race to the bottom for welfare standards - contrary to the wishes of the UK industry".
The peers also noted that much farm animal welfare research is backed by Brussels and "Brexit could lead to a major funding gap".
The sub-committee's chairman, Liberal Democrat Lord Teverson, said: "The UK has some of the highest farm animal welfare standards in the world and UK producers are rightly proud of those.
"We see no reason why Brexit should diminish those, as long as the Government is aware of the challenges ahead and acts accordingly."
He said the committee heard "evidence of undeniable concern that opening up the UK market to free global trade poses a number of issues" and "the Government may find it hard to reconcile its free trade ambitions with its commendable desire for preserving high farm animal welfare standards".
He added: "We heard overwhelming support for farm animal welfare standards to be maintained or improved.
"To help achieve that, we urge the Government to secure the inclusion of high farm animal welfare standards in any free trade agreements it negotiates after Brexit."
The committee said the prospect of UK producers competing with lower-welfare rivals meant there was a strong case for simplifying product labelling so consumers could know what they were buying.