The letter describes how to avert the curse

The letter, which encloses a Jack of Spades card, tells the recipient they have been cursed.

It goes on to tell them to destroy the card by ripping it into four and to return it enclosing "a modest donation of �10" to neutralise the curse.

Trading Standards said of the letter: "We have never heard about one quite as menacing as this."

Spin-off

The opening paragraph of the letter, which bears an Austrian address from a clairvoyant astrologer by the name of Samantha, says the Jack of Spades is "a symbol of treason and disaster that you must absolutely destroy in order to avert the curse!".

Cornwall Trading Standards said the letter appeared to be a spin-off from prize draws and prize competition scams.

Liz Rickard, of Trading Standards, said: "This letter is particularly nasty.

"Although we have received complaints about similar letters before we have never heard about one quite as menacing as this.