YouTube's prevalence across the Google platform and its easy integration across other content platforms has helped contribute to its rise.
This year, 40.4 million people, or six out of 10 people in the UK, are expected to watch video via the YouTube app or website at least once per month, eMarketer estimated.
However, YouTube is starting to face competition from subscription streaming services such as Netflix, Amazon Prime and Hulu.
These services have made digital video streaming commonplace in the UK. This year, more than two-thirds of the UK’s population will be watching some form of digital video.
In addition, almost two-thirds (64.3%) of digital video viewers in the UK are expected to view content via mobile phone. Subsequently, YouTube is competing for eyeballs from Facebook, Instagram and Snapchat, all of which have been investing heavily in video over the past few years.
As a result, while the absolute number of YouTube viewers are expected to continue to grow slowly in the coming years, the platform's share of digital video viewers is expected to decline gently from 90.6% to 90.3% in 2020.
"UK adults have been migrating their social media and video habits over to mobile for some time," eMarketer senior analyst Bill Fisher, said. "It’s no surprise, then, that the social media platforms have been making major plays in the video space. YouTube viewership isn’t going to drop away, of course—it’s too well-established. But it’s going to have to compete for video-viewing time from a multitude of other options like never before."