The deal, understood to be worth £25 million over the next five years, has been criticised by MPs and animal welfare groups.
The British Veterinary Association has called on the government to clarify whether the lambs would be killed using a ‘cruel’ non-stun method, which the body condemns as causing ‘unnecessary suffering’.
BVA President John Fishwick told Yahoo News: ‘The fact that we’ve got a trade deal for British lamb to Saudi Arabia is really good and we should welcome that. It shows the high quality of British produce.
‘The concern is that we don’t have clarity on whether or not these animals are going to be stunned when they’re slaughtered.
‘We have campaigned for many years that only animals that have been properly stunned should be slaughtered in the UK for any consumption – home consumption or for export.’
Currently the law in the UK and EU prohibits the slaughter of animals without stunning them first, but exceptions are made for a small number of religious communities.
It is understood that the lamb sold to Saudi Arabia will be certified by the Halal Monitoring Committee, which does not permit any form of stunning, according to Vet Record.
Mr Fishwick warned that a deal could suggest a lowering of welfare standards in the UK in the interests of increasing exports.
He said: ‘I think there is a danger that, if we’re willing to sign up to a major trade deal and all those animals are going to be slaughtered in a non-stunned method which we consider causes unnecessary suffering, that would be a very, very bad sign about standards here in the UK.’
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Tim Farron, the Liberal Democrat’s food spokesperson, also warned that the UK could see its standards slip.
He said: ‘This does not bode well, as post-Brexit the UK will inevitably receive pressure from new trading partners to open markets to low-welfare animal products.’
A Defra spokesperson told Yahoo: ‘Earlier this year, the Government announced it had reached an agreement with Saudi Arabia to lift the 20-year ban on lamb exports, which was introduced after the BSE crisis.
‘Whilst there are currently no restrictions on exporting non-stun meat, all slaughter – whether stun or non-stun – must strictly comply with EU and UK rules on animal welfare. We have been clear these standards will not be watered down as we leave the EU.’
A 2003 Farm Animal Welfare Council study found that killing livestock without stunning causes ‘very significant pain and distress’.
European Food Safety Authority said in a 2004 report: ‘The animals which are slaughtered have systems for detecting and feeling pain and, as a result of the cut and the blood loss, if not stunned their welfare will be poor because of pain, fear and other adverse effects.’