The latest AHDB Beef and Lamb Watch has revealed Tesco lamb facings for August 2015 have dropped by 15 per cent compared to August 2014, from 73 per cent to 58 per cent.
NFU livestock board chairman Charles Sercombe said the findings were ‘another kick in the teeth’ for struggling sheep farmers.
Mr Sercombe said it appeared the retailer was ‘saying one thing but doing another’.
“Using facings as a key indicator, Tesco support for domestic lamb is not just below average, but it appears to be bottom of the pile,” he said.
“We are challenging Tesco to explain how this reduction in the percentage of British lamb sold is compatible with its open public commitments to source more meat closer to home.
“British farmers are once again asking, why in the peak British lamb season are Tesco not backing British?”
At Tesco’s AGM in June, NFU president Meurig Raymond urged the retailer to demonstrate exactly how it wass delivering on its promises and commitments made at NFU Conference in 2013 and to give firm evidence that progress is being made.
At the time, Tesco said the promises to source more meat closer to home still stood.
The AHDB report said Waitrose, Budgens, Aldi and Morrisons all had 100 per cent British lamb facings.
The Co-operative, Sainsbury’s, ASDA and Lidl are improving their British offering, ‘but could do better’ according to Mr Sercombe.
National Sheep Association communications manager Joanne Briggs added: "It is disappointing to see Asda and Lidl on 74 per cent and 72 per cent respectively, but what is particularly poor is that Tesco has actually gone backwards since June, and it was only at 68 per cent then.
"The recent report shows that 58 per cent of product in Tesco was from Great Britain, compared to 73 per cent at the same time the year previous.
"This is not acceptable and, in what has been a difficult year for UK producers, does not provide the confidence that the industry needs. All retailers need to support UK producers in order to protect and build their domestic supply chain."
A Tesco spokesman said: "To ensure our customers have consistently high quality lamb available all year round we source from both the UK and New Zealand.
"We recognise the quality of British lamb and are proud to be the biggest buyer of it.
"New Zealand lamb is also recognised by customers as a great quality product and is consistently good value throughout the year. This helps us to keep lamb affordable for our customers and meet the demand for popular cuts."