More than half of UK readers of the Independent and the Daily Mirror access the sites only from mobile devices, according to the latest National Readership Survey figures released today.
Some 55.5 per cent of the Independent's audience read stories exclusively from mobile devices between April 2014 and March 2015, while at the Mirror 52.84 per cent of readers were mobile-only.
The Mirror also saw the highest number of mobile-only readers of all UK news outlets included in the NRS report, with 12 million out of almost 23 million total readers.
Pete Picton, Mirror Online's editorial director, told Journalism.co.uk in an email that the Mirror's mobile traffic growth, from a third of website visitors two years ago to over half now, has been driven partly by the outlet's increased activity on social media.
"We are seeking to build on this from both an editorial and product point of view.
"For example, introducing [new software] to our mobile site which enables readers to move seamlessly from one story to another, and editorially, providing more breaking news with liveblogs and adding interactive elements such as polls to stories.
He said some of most popular pieces on mobile and social have been celebrity stories and breaking news.
"[And] as a general rule, breaking news and photos will increase the traffic a story obtains."
The Times and The Sun have the lowest proportion of mobile-only web readers at just 8.2 and 4.4 per cent respectively.
Both News UK titles operate a hard paywall on access to the website, largely restricting mobile viewers to their app.
The Daily Mail continues to attract the biggest audience with 29 million average monthly UK readers, followed by The Daily Mirror and the Guardian with 22.9 million and 21.6 million UK readers respectively.
The Guardian leads the way in UK digital news, with 94.4 per cent of its total audience accessing its stories from a PC or mobile device, compared to 93.4 per cent at the Independent and 91 per cent at the Telegraph.
And at the Guardian, the Independent and the Daily Mirror, two thirds of the full UK audience reads news on mobile – 66 per cent, 69 per cent and 67 per cent respectively, including those who also read the outlets' stories in print or on desktop.
The Daily Mail and the Daily Telegraph are both approaching this mark too, with around 65 per cent of their audience using mobile devices for news at the moment.
The PADD: Mobile report combines NRS data from April 2014 to March 2015 with comScore data from March 2015, and this is the first time mobile estimates from comScore have been included.
From 2016, the NRS will be replaced by a new audience measurement company, as chief executive Simon Redican says it's time to "start afresh".
"When your starting point was 60 years ago in a print-only world, a mindset change is needed," he told Journalism.co.uk in April.