The Porkwatch survey, which is conducted every two months, records the number of product lines that supermarkets allocate to British pork and pork products.

All retailers have increased their British lines in some categories and some have improved across the board, selling more British pork, bacon, ham and sausages.

"These results show that retailers are listening to their customers," said National Pig Association acting general manager Lizzie Press. "We are delighted with the current trend because it is allowing pig farmers to reinvest in their businesses after three very difficult years caused by high feed costs."

NPA chairman Richard Longthorp said, "Shoppers often used to choose British meat where possible, but Horsegate has proved a game-changer and now many are insisting it must be British.

"We are grateful to retailers for the way they have stepped up to the mark, even when cheaper imported product has been available."

The most recent Porkwatch survey shows the following year-on-year improvements:

• M&S, Aldi and Budgens have more British pork, bacon, ham and sausage lines than at this time last year.
• Waitrose has more British pork, ham and sausage lines, and has maintained its number of British bacon lines.
• Morrisons has more British pork, bacon and sausage lines and the Co-op has more British pork, ham and sausage lines.
• Sainsbury's has more British ham lines and has increased its British pork lines by 19 per cent to 100 per cent.
• Tesco, Asda and Lidl all show an improvement in their number of ham and sausage lines.

Overall British ham shelf facings are up 3.9 per cent year-on-year, whilst sausages are up 3.5 per cent and pork is up 1.5 per cent (from an already high base). But bacon is down 7.4 per cent and NPA will be urging retailers to improve their number of British bacon shelf facings in 2014.

Notable among retailers for their long-term support of British-farmed meat are Waitrose and M&S, both achieving 100 per cent British, or very near it, in all pork and pork product categories.

The Porkwatch survey is conducted on behalf of English pig industry levy board BPEX.