"The email is an absolute hoax and we are urging our customers to delete it and not send it on to anyone they know, " a spokeswoman for Marks and Spencer told the Sunday Tribune. "Some unknown person has attempted to cash in on our name and it is nothing to do with us."

The email, which made its way to Ireland last week, advises recipients that "Marks and Spencers are trying word-of-mouth advertising to introduce its products and the reward you receive for advertising for them is non-refundable vouchers to be used in any M&S store. To receive your free vouchers by email, all you have to do is send this email to 8 people (for �100 of free vouchers) or 20 people (for �500 of free vouchers)."

M&S has received "a number of calls" in relation to the email, which several people believed to be genuine. UK estate agent Persimmon Homes is also referred to in the email and it issued a statement last week denying all association with the offer.

"Our customer service team have been briefed to deal with any queries in relation to this incident and we think the confusion should die down very soon, " said the M&S spokeswoman. "We are currently investigating the source of the email, but have been told it will probably be very difficult to track the person down."