Nielsen IAG aims to quantify how closely viewers are paying attention to programmes and adverts, adding valuable information to traditional ratings that simply show how many people were watching. The system works by surveying a panel of TV viewers each night on how well they recall the details of programmes and ads they have seen in the last 24 hours.

IAG was founded in 1999 and bought by Nielsen for $225m in 2008. Its service has been available for some years in the US, where networks use the data in their negotiations with advertisers.

Alan Gould, co-CEO of Nielsen IAG, said the service will help UK advertisers “make smarter decisions” about which programmes and ads are performing best. “We’ll see advertisers buying TV spots increasingly on the basis of how engaged the audience is not just how big it is,” he said.

Darren Moore, vice president of research at IAG, said: “We’ll give advertisers prompt insights into how their ad is performing… they’ll also quickly be able to match up effective ads with programmes with high engagement.”

First results showed that the most remembered ad for the month ending 21 February was for Colgate toothpaste, while the ad with the strongest brand recall was for Mr Muscle.