Sainsbury’s has blocked the majority of voucher codes on its website, after mischievous customers found they could get massive discounts through a loophole in its coupon campaign.

The supermarket clearly hasn’t learned the lessons provided recently by toy retailer Hamleys, whose warehouses were almost stripped bare by discount-hungry consumers in the week before Christmas. 

On that occasion, Hamleys, after originally saying it would honour the discounts, backtracked and cancelled the orders, blaming a ‘technical error’ on its website. It did at least sweeten the pill by offering those customers a 25% reduction as a goodwill gesture.

By contrast, Sainsbury’s has bitten the bullet and cancelled the discounts, saying it will stop the use of most voucher codes on its site.

It has blamed the problem on unscrupulous web users taking advantage of voucher codes that are intended for single use, but end up being posted on internet forums and circulated by email.

The vouchers are even available to buy on eBay – showing yet again how mistakes in online discount campaigns can be rapidly picked up on and spread before they can be put right.

As we reported last week, voucher company Couponstar and several UK portals are planning to launch a network for promotional campaigns, which aims to increase the reach of vouchers for retailers, as well as offering them better security.