According to new rankings released by the Kantar Media company AdGooroo, the retailer generated almost 35 million clicks, over 8.5 million more than the next advertiser in the ranking.
The study ranked the top 20 UK paid search advertisers based on Google.co.uk desktop text ad clicks on the top 50,000 keywords between January and December 2016.
Companies featuring prominently in the top 20 include travel brands booking.com, which came in second place, and onthebeach.co.uk, Trivago, Expedia and Airbnb.
Retailers in the top 20 rankings list include ASOS, JD Sports, Boots, John Lewis and Asda.
Eric Marcy, chief revenue officer at AdGooroo, said: “Our findings not only reveal the top paid search advertisers in the UK but also mirror the most popular industry sectors in the UK market: retail, travel and financial services. In particular, the presence of so many travel brands at the top of the ranking highlights a particularly competitive market for companies in this sector.”