Legal advisers to Britain's Churches have sent out a circular saying that while people can use jars for jam at home or to give to family and friends, they cannot sell them or even give them away as raffle prizes at a public event, the MailOnline reported.
The circular from the Churches' Legislation Advisory Service is pointedly headed: "Please take note: this looks like a spoof but it's not."
The advisers say the rules that are being breached are the snappily-titled EC Regulations 1935/2004 and 2023/2006, which prevent containers being re-used unless they are specifically designed for that purpose.
The Food Standards Agency said that the rules had been introduced because there was a risk of chemicals leaching out of old containers and contaminating food, though it added that it was not aware that re-used jam jars were a safety hazard.
The agency said it was up to local authority to enforce the regulations, and penalties can reach a maximum of a 5,000 pounds fine, six months' imprisonment, or both.
The news will alarm the growing number of jam-makers inspired by model Kate Moss, who makes damson jam out of fruit from her Cotswolds estate, and the Duchess of Cambridge, who keeps pots to give away to friends.