LONDON/BERLIN: Programmatic trading is surging ahead in Europe, but the rate of online ad viewability has declined, most notably in the UK, two new reports have indicated.

Adform, a Danish digital advertising insights firm, reported that ad space bought via programmatic trading increased 76% year-on-year to April 2015, driven to a large extent by a 333% rise in spend on branding ad formats.

This led to an increase of 119% in total adspend, the report said, as advertisers dedicated a larger proportion of their budgets to programmatic channels.

However, despite brand advertisers paying more attention to programmatic, ad viewability across Europe declined 0.7% to 55% over the past year. There was a marked decline in the UK, the report noted.

Meanwhile, the overall engagement rate in Europe fell by 33% while the average engagement time spent with ads declined to 12.66 seconds from 13.93 seconds.

The drop in ad viewability rates over the last year occurred despite guidance from the Internet Advertising Bureau (IAB) aimed at raising viewability standards.

Further evidence about the ongoing problem came in a separate report from German ad verification company Meetrics, which reported that the level of online ad viewability in the UK had "dropped noticeably over the last year".

Only 49% of online ads in the UK during Q2 2015 met the IAB's recommendation that an ad is considered viewable if 50% of it is in view for at least one second. That compared with 56% in Q2 2014.

Interestingly, viewability rates were considerably higher in Germany (64%) and France (62%) where the programmatic marketplace is less advanced.

"There's no doubt programmatic brings many benefits to advertisers but there's a flip side to every coin," said Anant Joshi, director of international business at Meetrics.

"It's certainly less transparent than buying directly and there's also a big question mark about the quality of much of the inventory sold this way and, clearly, that most of it never ends up being seen."

Data sourced from Adform, Meetrics, IAB; additional content by Warc staff