A cafe chain that serves food destined for landfill may face prosecution for selling out-of-date produce.
West Yorkshire Trading Standards (WYTSS) said it found more than 400 items past their use-by date at the Real Junk Food Project's (RJFP) warehouse in Pudsey, Leeds.
Project founder Adam Smith said it had made "food unfit for human consumption available to the general public" since 2013 without complaint.
WYTSS said it was unable to comment.
The letter states 444 items, which were a cumulative total of 6,345 days past the use-by dates, were discovered at the charity's premises on the Grangefield Industrial Estate.
It said Mr Smith was invited to attend a "formal recorded interview under caution" to discuss offences which may have been committed under the Food Safety and Hygiene (England) Regulations 2013.
Mr Smith said: "[The letter] was claiming that we were making food unfit for human consumption available to the general public, which is true, because that's what we've done since day one when we opened three-and-a-half years ago.
"We've got 127 cafes in seven countries across the world. We've fed over one million people worldwide with food that's expired and still to this day no-one has ever been sick. So we can prove that we can make this food safe for human consumption.
"I'm quite positive about it. Just because it's the law doesn't make it right. We can prove that the food is safe for human consumption.
"We're not going to stop serving food to people that's expired because it will then go to waste and that's the reason that we're here."
He said he hoped the meeting would help create a debate around the legislation
David Strover, from WYTSS said: "I am sure you will appreciate that WYTSS is unable to comment on the detail of an ongoing investigation except to say that the Proprietor of RJFP will be able to put forward information as part of that investigation process.
"That will help inform the decision on what, if any, action will be taken."
Mark Jones, solicitor and food and drink specialist with West Yorkshire law firm Gordons, said the charity may find it difficult to contest any case brought against it.
He said: "If you pass a use-by date, the starting point is that the food is unsafe and the law expressly says that. If they have been using food which is past its 'use-by' date RJFP will struggle to find a defence.
"The law is European law implemented by domestic legislation and is not something that can be sidestepped.
"If RJFP have been selling food past its use-by date unlawfully, the extent to which they have actively engaged in this practice will determine the outcome of any prosecution; that could be a fine if it's significant or even a prison sentence.
"One thing that is likely to influence trading standards is the nature of the business. This is not a situation where you have an individual seeking to make vast commercial profit by selling out-of-date food, it's a charitable organisation seeking to reduce food waste which it seems may have fallen foul of technical food regulations."