Furious Waitrose super-market bosses have banned the sale of the batches and have severed all business ties with the Irish owners of Freshlink.
Food inspectors have launched a major probe at the East End site after the supermarket chain told how it had found suspect batches.
The latest scare came as Westminster's Environment Secretary Owen Paterson flew to Brussels for an emergency summit on horse meat after a slaughterhouse and meat manufacturer in Britain were raided and shut down.
Today it was claimed some tests had revealed that "beef-only" meatballs made at the closure-threatened Freshlink site at Shettleston contained traces of pork. The suspect batches were produced last summer and supplied to food store chain Waitrose.
The affected batches were labelled Frozen Essential Waitrose Meatballs – 16 British Beef Meatballs 480g. One was marked Best Before End June 2013 and the other Best Before End August 2013.
In an open letter to customers, Waitrose managing director Mark Price said: "We have now done tests on 40 of our meat products, no horsemeat was found in any of these tests.
"We did, however, discover that in just two batches of our essential Waitrose frozen British beef meatballs (480g), some of the meatballs may contain some pork.
"In fact, one of the tests carried out showed that the meat in the meatballs was, as it should be, 100% beef.
"But because another test indicated there may be some pork, I felt it important for you to be aware."
"At Waitrose, the welfare of animals and quality of our fresh and frozen meat has always been of the highest priority.
"That is why we have just announced that in partnership with our dedicated beef supplier, we will create a new facility which in addition to supplying all of our fresh beef, will also now produce a range of frozen Waitrose beef products.
"All the beef processed at this site will continue to be sourced from our known and trusted group of British farmers."
Waitrose also said it had now ended all business ties with the ABP, which owned the Glasgow factory and is currently switching all production to England with the loss of more than 200 jobs.
Responding to the claim, an ABP spokeswoman said: “Freshlink has carried out over 450 DNA tests during the last two and a half years. All our test results have been confirmed as negative for non-declared species.
“Freshlink will share all results directly with the Food Standards Agency (FSA) as part of their investigations.”
The Food Standards Agency in Scotland said local safety inspectors from Glasgow City Council "regularly" visit the Freshlink factory to take samples "but the results have not yet been received".
The latest scandal to hit the food industry comes after police and watchdogs swooped on a slaughterhouse in West Yorkshire and a meat manufacturer in Wales to investigate claims they supplied horse carcasses in burgers and kebabs.