Sainsbury’s has signed a deal with one of its old foes that will transform the way the supermarket runs promotions and handles online discount vouchers. Eagle Eye, the virtual voucher business backed by former Tesco boss Sir Terry Leahy, will announce today a “game-changing” contract with Sainsbury’s that will handle its digital coupons across its grocery empire. Eagle Eye’s software will be rolled out across Sainsbury’s supermarket tills to register discount vouchers on shoppers’ phones. The UK coupon market is worth £1.6bn after rising 100pc in value over the last five years. However, while consumers used to rely on newspaper-printed vouchers, or postal promotional letters, there has been a surge in shoppers using their mobile phones to download vouchers or access them through apps and emails.