The House of Commons has voted against transferring an EU clause which recognizes 'animal sentience' into domestic law - leading some to fear animals could become 'collateral damage' after Brexit.
But the move was rejected by a slim majority of 18 for the Government - only 295 were in favor, with 313 against.
Under EU law, animals are recognized as sentient beings with feelings - and the Lisbon Treaty says this must be taken into account when creating policy that will affect them.
The clause Lucas wanted to transfer into UK law says: "In formulating and implementing the Union's agriculture, fisheries, transport, internal market, research and technological development and space policies, the Union and the Member States shall, since animals are sentient beings, pay full regard to the welfare requirements of animals, while respecting the legislative or administrative provisions and customs of the Member States relating in particular to religious rites, cultural traditions and regional heritage."
As MPs have voted not to transfer the clause to domestic law, some groups are concerned about the impact this could have on animals post-Brexit.
British Veterinary Association Senior Vice President Gudrun Ravetz said: "It is extremely concerning a marginal majority of MPs have voted down this seminal clause.
"Enshrining animal sentience in UK law would have acknowledged that we consider animals as being capable of feelings such as pain and contentment and, so, deserving of consideration and respect.
"It is a founding principle of animal welfare science and the way we should treat all animals.
"As an animal welfare-led profession, the BVA has been calling on the Government to at least maintain standards of animal health and welfare and public health. Yet, actions speak louder than words, and this action undermines the Government’s previous promises the UK will continue to be known for our high standards of animal health and welfare post-Brexit.
"There is an urgent need for clarity from the Government on how the provisions in Article 13 will be enshrined in UK law to ensure we do not fall short of the high standards we expect as a nation of animal lovers."
During the EU debate that preceded the vote, the Government argued that transferring the clause was unnecessary, as animal sentience is covered already by EU law - in the Animal Welfare Act 2006.
But welfarists have argued this is not the case.
RSPCA Head of Public Affairs David Bowles said: "It’s shocking that MPs have given the thumbs down to incorporating animal sentience into post-Brexit UK law.
"Animal sentience is never mentioned in the Animal Welfare Act and, crucially, only domestic animals are really covered by the provisions of the Act anyway and animals in the wild and laboratories are expressly exempt.
"It is simply wrong for the Government to claim that the Act protects animal sentience.
"In the EU, we know that the recognition of animals as sentient beings has been effective in improving animal welfare across the region.
"If the UK is to achieve the Environment Secretary’s objective of achieving the highest possible animal welfare post-Brexit, it must do the same."
Out of step
Dr. Toni Shephard, Executive Director (UK) of animal protection group Animal Equality, told PBN: "This is a truly shocking and extremely worrying move which is completely out of step with public opinion.
"Most British people share their home with a cat or dog, guinea pigs or rabbits, even hens or rats, and know full well the complex range of emotions and feelings these animals - and all animals - experience.
"This retrograde step could pave the way for the UK to scrap animal welfare laws which originate in EU legislation and makes a complete mockery of the government’s incessant claims that we are world leaders in animal welfare.
"It is absolutely disgraceful and shames us on the world stage."
Following the defeat, Lucas said: "The decision by the Government to vote down my amendment on animal sentience really was disappointing.
"This change would have guaranteed animals don’t become collateral damage in the Brexit negotiations – and it’s a real shame it was rejected.
"I know animal lovers will be concerned by this setback, but there’s still a chance the House of Lords can change the bill – and enshrine animal sentience into British law."