The year-long research project involving the FMCG companies, along with i2c, Nielsen, Nectar and the Internet Advertising Bureau UK (IAB) found that every £1 spent on online display ads delivered an average of £1.94 in sales.

The study tested ads for nine consumer goods brands – Nescafé, Häagen Dazs, Persil, PG Tips, Magnum, Surf, Maille, Tropicana and Aquafresh – across mainstream desktop and mobile websites including the Guardian, Yahoo!, eBay, Gumtree, AutoTrader and Mail Online.

Purchase behaviour was analysed using a combination of Nectar loyalty card sales data for 12m Sainsbury’s customers, and Nielsen Homescan data, which measures shopping behaviour at UK supermarkets through a panel.

Tim Elkington, chief digital officer at the IAB, said that “the vast majority of sales” that were attributed to the online ad occurred in store.

He added: “The calibre and range of the brands involved in the project gives marketers a reassuring guide as to what their investment in digital will pay back.”

The study was commissioned by i2c, a partnership between Sainsbury’s and Aimia (the owner of the Nectar loyalty programme). All of the ads tracked carried a Sainsbury’s logo. According to a post-campaign survey of 1,200 British adults from i2c, 38% said seeing the Sainsbury’s logo would make no difference to which supermarket they purchased the brand from.

Online ads also had a positive effect on awareness of and favourability towards the brand in question, according to the research, which found that people who had seen the ads were 12% more likely to consider the brand to be ‘premium’.