Question: What was the most watched documentary in 2016?

List of most watched television broadcasts in the United Kingdom

In the United Kingdom, viewing figures – the number of viewers or households watching a television programme, have been recorded by the Broadcasters' Audience Research Board (BARB) since 1981. Prior to the board's formation, figures were conducted by different means such as the BBC financing its own audience research, while the ITV companies sub-contracted theirs.
Most watched special events
The majority of special events attracting large audiences are often carried on more than one channel. The most watched programme of all time on a single channel is the 1973 wedding ceremony of The Princess Anne, shown only on BBC1.
Post-1981 figures verified by the Broadcasters' Audience Research Board (BARB)
Pre-1981 figures supplied by the British Film Institute (BFI)

Notes:
At least two Muhammad Ali boxing matches were reported to have been watched by at least 26million viewers in the United Kingdom: the Fight of the Century (Ali vs. Frazier) was reported to have been watched by 27.5million British viewers in 1971,[7] and The Rumble in the Jungle (Ali vs. Foreman) was reported to have been watched by 26million viewers on BBC One in 1974.[8]
Live Aid is reported to have reached approximately 24.5million British viewers in July 1985.[9]
The Wedding of Prince William and Catherine Middleton (29 April 2011) received a total audience peak of 26 million viewers, but this is a combined figure aggregated from the ten different channels that broadcast the ceremony. The highest figures of these were 13.59 million on BBC1, with an extra 4.02 million watching on ITV.[10]
Most watched programmes
The following is a list of most watched programmes, excluding sporting events and news coverage. The mid-1980s introduction of in-week repeat showings accounts for six of the top ten programmes. On this measure, the 1996 Christmas edition of Only Fools and Horses is the most watched non-repeated, non-documentary programme of all time in the United Kingdom. It is the third most watched programme of all time on a single channel, after the 2012 Summer Olympics closing ceremony and the wedding of Princess Anne and Mark Phillips in 1973 (see below).
Post-1981 figures verified by the Broadcasters' Audience Research Board (BARB)
Pre-1981 figures supplied by the British Film Institute
Key
  Numbers with this background and symbol are italicised to denote aggregated figure with repeat showing.

Most watched films
These are the most watched films by total number of viewers[17] (dates are when the films were broadcast, not necessarily when they were produced).

Most watched broadcasts by year


Notes
 – The Royal Wedding of Prince William and Catherine Middleton (29 April 2011) "attracted a consolidated average audience of 26.0 [million] viewers across the ceremony from 11:00am to 12:10pm. This is an aggregated audience across 10 BARB reported channels that followed the events live."[49] The highest figures for individual channels of these were 13.59million on BBC One, followed by 4.02million watching on ITV.
 – The 2014 FIFA World Cup Final was broadcast by both BBC One and ITV. The highest figures were 14.96million on BBC One, followed by 2.34million on ITV.