Retail giant Gap Inc is warning that its 30% off discount vouchers for the UK have been altered into fake 60%-off ones.

The company had originally emailed 30%-off vouchers to associates in the UK for the holiday period, before doctored versions began to appear. It is thought that the original voucher was printed off, altered and then re-scanned.

A spokesperson for Gap told just-style: "We've heard that there are vouchers offering 60% off at Gap in circulation. These are a hoax, not issued by Gap and will not be honoured. We apologise to our customers for any inconvenience caused.

"For background, there is a genuine offer of 30% discount available in Gap stores in Europe for a short time period that has been offered to a very limited number of friends and family of Gap employees, as well as a handful of companies that Gap has a relationship with.

"It would appear that this genuine offer has, in some instances been fraudulently altered."

It follows similar instances last year, notably a voucher offering 40% off drinks retailer Threshers that was circulated beyond the company's expectations, but was still honoured.