IN BRITAIN’S BIGGEST loyalty promotion yet, J Sainsbury is offering its fourteen million Reward Card -holders a £100 discount on their summer holiday. The offer, which runs May through June, is expected to pay-out up to £900 million in discounts on a range of European and American holidays selected from the brochures of participating holiday companies including First Choice, Sovereign and British Airways. Retail analysts predict a marked increase in consumer spending at Sainsbury as cardholders accrue the 500 bonus points needed to qualify for the offer. Rival supermarkets are expected to retaliate with equally tempting offers. Said a Sainsbury spokesperson: 'This will raise the stakes even higher on discounts offered by supermarkets. We just wanted to reward our loyal customers. It will be interesting to see what the others do now.' The promo is also boosted by a massive giveaway of one million Air Miles to all shoppers using their card during the promotional period. There are four main prizes of 30,000 miles - each sufficient for a round trip to Australia.