Rogue McDonald's managers in Norfolk ordered staff to prepare food in their own homes and bought stock from nearby supermarkets, it can be revealed.
A former employee at the Hoveton fast food restaurant has blown the whistle on some of the methods used including staff chopping up vegetables in their own kitchens and dashing out to buy hash browns from the Co-Op.
And messages and pictures given to this newspaper record managers at the global fast food outlet asking employees to buy food from the Roys of Wroxham foodhall next door.
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Other messages show bags of hash browns purchased from the Co-Op. A bag of frozen hash browns costs approximately £1.50 whereas a single one at McDonald's retails for 89p.
Another picture shared on the WhatsApp group shows a pile of red onions chopped in an employee's kitchen - which was not subject to the usual rigorous hygiene standards of a commercial kitchen.
The whistleblower, who asked to remain anonymous, said: "What was really worrying to me was the fact that we were advertising food as being safe for people with nut allergies. But food was being prepared in homes where people ate nuts and obviously these kitchens didn't have the same hygiene levels.
"I watched a documentary about the girl who had a really serious nut allergy and died after eating a mislabelled sandwich. I just couldn't bear to be involved in it any more so I handed in my notice."
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A spokesman at McDonald's said: "Having investigated, we can confirm that this took place on a small number of occasions. The practise was stopped immediately when senior management became aware and appropriate action was taken. We work only with select approved suppliers."
The source alleged that "practically all" of the ingredients needed for the restaurant were in the past purchased from nearby shops at some point.
"The problem was you could only bulk order items. Coleslaw, for example, would come in packs of ten boxes even though we only needed three. We ended up wasting loads," the source said.
"Instead of having one of us drive to another store and give the surplus stock to them, the manager would just tell us not to order any in and would tell us to go and buy top ups in town."
The source added that when they left the company they raised the issue with management.
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