Sainsbury's, the UK's third-largest grocer, heightened its promotional activity during May, according to the latest just-food Promo Tracker.

The retailer increased the number of promotions in its stores from over 6,500 in April to over 8,200 in May. The jump meant that the proportion of SKUs on promotion at Sainsbury's outlets rose from 28.1% in April to 34.8% in May.

Asda, the UK's number two retailer, also upped the number of products sold at a discount in May. The increase meant Wal-Mart Stores' UK arm sold 23.1% of its SKUS on promotion in May, up from 22.9% in April.

Tesco and Ocado - the two other retailers measured by the Promo Tracker, which is developed in conjunction with mysupermarket-insights.co.uk - cut the number of promotions they ran in May.

Frozen pizza and bread was the most-promoted category, with 54.4% of SKUs on promotion. The second and third most-promoted categories were yoghurt and yoghurt and milk drinks respectively, which led to Danone's Activia and Actimel brands being the two most-promoted brands in May.

In terms of brands, Muller yoghurt was third, followed by Campbell's soup in fourth and baby food brand Plum Baby in fifth.

Supermarket Total number of SKUs Number of Promos % of all SKUs on promo Average saving per promo
Tesco 33023 11955 36.2 £1
Asda 28907 6687 23.13 £0.56
Sainsbury's 23810 8281 34.78 £1.15
Ocado 20825 4830 23.19 £1.04
Category % of all SKUs on promo Average saving per promo
Frozen Pizza & Breads 54.43 £0.53
Yogurts 53.53 £0.27
Yogurt & Milk Drinks 52.48 £0.48
Chilled Desserts 49.28 £0.28
Chocolate Biscuits 49.2 £0.51
Baby Food & Snacks 48.79 £0.22
Frozen Vegetarian 48.4 £0.49
Crisps 43.97 £0.49
Cooked, Prepared Meat & Poultry 42.28 £0.54
Ice Cream 42.11 £0.79
Sausages & Burgers 39.78 £0.52
Fresh Pizza & Chilled Bread 38.99 £0.59
Fresh Herbs 37.5 £0.24
Fruit 35.95 £0.71
Snack Meals 35.92 £0.25
Biscuits 35.77 £0.49
Tinned Pasta 34.74 £0.15
Packet Soup 34.55 £0.22
Frozen Ready Meals 34 £0.48
Crackers 32.95 £0.36
Brand % of all SKUs on promo Average saving per promo
Actimel 95 £0.56
Activia 83.2 £0.19
Muller 81.6 £0.38
Campbell's (Soup & Mixes) 76.7 £0.25
Plum Baby 72.6 £0.45
Pringles 72.5 £0.8
72.4 £0.93
Ben & Jerry's 70.3 £1.5
Tilda 64.2 £0.69
Bassett's 63.9 £1.33
Walkers (Crisps, Snacks & Dips) 63.3 £0.4
Pot Noodle 59.7 £0.35
Fox's (Biscuits) 59.5 £0.52
McVitie's 59.1 £0.5
Rachel's 58.5 £0.22
Pizza Express 57.6 £0.73
Tesco Italian 56.6 £0.42
Hipp 55.9 £0.24
Alpro Soya 54.9 £0.34
Wall's (Ice Cream) 54.9 £0.86