1 Friends Comedy Sitcom Acquisition Netflix USA 2.38%
2 The Grand Tour Entertainment Magazine Original Amazon UK 2.03%
3 You Drama Thriller Original Netflix USA 1.86%
4 The Good Place Comedy Sci-Fi/Fantasy Original Netflix USA 1.63%
5 Brooklyn Nine-Nine Comedy Sitcom Acquisition Netflix USA 1.53%
6 The Big Bang Theory Comedy Sitcom Acquisition Netflix USA 1.42%
7 Luther Drama Crime Acquisition Netflix UK 1.34%
8 Marvel's The Punisher Drama Superhero Original Netflix USA 1.29%
9 Suits Drama Legal Acquisition Netflix/Amazon USA 1.29%
10 The Office (US) Comedy Sitcom Acquisition Amazon USA 1.18%
11 Vikings Drama Action/adventure Acquisition Amazon Canada/Ireland 1.14%
12 Breaking Bad Drama Crime Acquisition Netflix USA 1.11%
13 Peaky Blinders Drama Crime Acquisition Netflix UK 1.05%
14 Grace and Frankie Drama Comedy Original Netflix USA 1.02%
15 Sex Education Drama Comedy Original Netflix UK 0.96%
16 Chilling Adventures Of Sabrina Drama Sci-Fi Fantasy Original Netflix USA 0.94%
17 Prison Break Drama Crime Acquisition Netflix/Amazon USA 0.87%
18 The Last Kingdom Drama History Original Netflix UK 0.84%
19 Orange is the New Black Drama Comedy Original Netflix USA 0.83%
20 The Umbrella Academy Comedy Superhero Original Netflix USA 0.79%

Full list is in the report at "UK", about halfway down the page:

https://www.ofcom.org.uk/research-and-data/tv-radio-and-on-demand/media-nations-2019