Some 56.9 per cent of Independent readers access the title only from their smartphones or tablets, followed by 53.2 per cent at the Daily Mirror, 51.5 per cent at the Express and 50.7 per cent at the Guardian.
The Independent and the Daily Mirror continue to grow their mobile-only audience, up from 55.7 per cent and 52.8 per cent respectively from last quarter, while the Guardian and the Express reached the milestone for the first time.
The Telegraph is not far behind with 49.3 per cent, up from 44.8 last quarter.
The digital audience at the Express has been on the rise in recent months, with the title reaching over 1 million daily readers for the first time in June, and again in July, according to figures from the Audit Bureau of Circulation.
Geoff Marsh, group director of digital content at Northern & Shell, told Journalism.co.uk in June the growth in digital audiences is the result of investments over two years after being "late to the digital party".
"The best way to do it is to work out strategically where you want to grow and where you want to be in 5 to 10 years time," he said.
The Guardian and the Independent also have the highest percentage of digital readers as part of their total UK audience, with 94.8 per cent and 92.36 per cent respectively, followed by the Telegraph with 91.6 per cent.
In contrast, The Sun and The Times have the lowest share of digital readers, and both titles operate a paywall limiting access to their websites.
NRS reports the Sun's digital readership as a 19.4 per cent share of the UK total, up from 15.6 per cent last quarter.
The Sun has also recently started to look into relaxing its paywall and making certain types of content available online for free, looking to take advantage of the rise of news publishing on social media.
At The Times, 20 per cent of its UK audience read the title online, slightly down from 20.4 per cent last quarter.
The Daily Mail remains overall the most read in the UK, with 29.5 million total readers, followed by the Mirror (23.3 million), the Guardian (22.9 million), and the Daily Telegraph (21.3 million).
The NRS PADD Mobile & Tablet report includes combined NRS data between July 2014 and June 2015 and comScore numbers from June 2015. The National Readership Survey is set to be replaced by a new measurement company from next year.
Free daily newsletter
- How publishers can tell better stories for mobile audiences
- Advice from 24 news organisations to help you tailor your story pitches
- Tip: Check out this toolkit for shooting 360-degree video on mobile
- Through VR project The Party, the Guardian is giving viewers an insight into living with autism
- Media's focus on technology tends to be short-term, shows survey