TV viewing on other devices accounts for only 1.5% of total viewing in the UK

"Analysis of UK TV viewing figures for the first half of 2013 shows how people’s TV diet is developing as on-demand TV viewing becomes a more established part of people’s lives.
According to Thinkbox, the marketing body for commercial TV in the UK, total average daily TV viewing in the UK during January-June 2013 was 4 hours, 1 minute a day per person.
This comprised:
3 hours, 58 minutes a day of linear TV on a TV set. This is 3 minutes a day less than the same period last year (source: Broadcasters’ Audience Research Board [BARB]). One reason for the slight drop is the improving economy.
3 minutes, 30 seconds a day via devices such as tablets, smartphones and laptops (or just over 3 half-hour TV shows a month). This is mostly on-demand but some live streams (source: figures supplied by UK broadcasters to Thinkbox).
In total, viewing on non-TV set devices via established services such as ITV Player, Sky Go, 4OD and BBC iPlayer, and new services such as Dave On-demand, accounted for 1.5 per cent of overall TV viewing during the first half of 2013. This is a slight increase on the full year figure for 2012, when it accounted for 1.2 per cent."

Source:  Advanced Television, 23rd August 2013