ASDA and Sainsbury's have been named and shamed in a new survey on how Scottish beef burgers in supermarkets are.

A new secret shopper study overseen by the National Farmers Union in Scotland found that only 40% of burger packs in supermarkets were labelled as Scottish.

And the research singled out Asda and Sainsbury's for criticism saying it was "surprising" that Scottish burgers were hard to find in two of the nation's largest retailers.

At Sainsbury's in Gyle in Edinburgh, the shoppers discovered 154 burger packs, and all were marked British.

READ MORE: 'Significant shortage' of Scottish pork on supermarket shelves with German chains biggest supporters, study

In visits to Asda in Fraserburgh, Kilmarnock, Edinburgh, Huntly and Peterhead, of 293 burger packs found just 17 were marked as a Scottish product, while 196 were labelled British.

Aldi and Tesco topped the chart for the availability of Scottish burgers with 86 per cent of packs in Aldi and 72 per cent of packs in Tesco.

While the shelf watch focused on supermarket own-label packs, those taking part in the secret shopper project also told NFU Scotland that some branded products were carrying unclear origin labelling despite the brands claiming association with Scotland.

The results come a week after it emerged Scottish farmers were losing £200 on every head of cattle they rear.

Beef prices have hit a three-year slow as consumers, wary of Brexit, switch to mince and cheaper cuts.

NFU Scotland, which has 8000 members, said the slump was so serious that it was putting the future of many family farms and crofts in doubt.

Commenting on the results NFU Scotland livestock committee chairman Jimmy Ireland, a beef farmer from Ayrshire, said “The good news here is that the general public can find Scottish burgers available in most supermarkets in Scotland. However, it’s surprising to see that they were hard to find in two of the nation’s largest retailers, Asda and Sainsbury’s.

“With farmers struggling to make any return from the market at the moment the message is clear that people should back Scotch Beef as much as possible this barbecue season.

“There was some unclear mixed origin labelling found on own-label products in Asda as well as on branded products not included in the survey. This once again demonstrates the need to increase transparency of origin labelling to ensure shoppers have the information they need to choose Scotch every time.

READ MORE: Ten of the most unique Scottish food brands

“NFU Scotland has sent the results of the shelf watch to all the major retailers to make them aware of the results. I would urge those retailers with only limited Scottish product available to increase their offering.”

The shelf watch is part of a six week campaign from the NFU which aims to encourage shoppers to look for Scottish beef during their next trip the shops, with the hashtag #BackScotchBeef.

The secret shoppers counted over 2,500 packs of burgers across some of the largest national grocery chains.

In April another secret shopper survey found there was a "significant shortage" of Scottish pork on shop shelves.

The NFUS research found that German supermarkets Aldi and Lidl were the biggest supporters of Scottish-labelled pork.

A similar exercise in August found that the they were also best at supporting Scottish lamb, with all produce sold being marked Scottish.

In 2017, campaign group Keep Scotland the Brand was launched, prompted by the steady disappearance of the Saltire on Scottish-grown food, and its replacement by Union flag packaging.

The #KeepScotlandtheBrand movement has been growing after fed-up customer Ruth Watson began tweeting pictures of Scottish products in supermarkets packaged under a Union flag.

An Asda spokesman said: “We always look to offer our customers the best possible value and we are proud to stock Scottish beef in our stores, which we continue to increase year on year”.

A Sainsbury's spokesman added: “We stock many Scotch beef products and offer a range in Scotland as well as across the rest of the UK.”