The Guardian drew in 3m UK unique users in April this year, which was up 24% from April 2007. It was closely followed by Telegraph.co.uk, which recorded 2.7m UK unique users, a rise of 77% year on year.
These figures correlate with last week's ABCe's, which indicated that the Guardian attracts a greater number of UK users, despite the Telegraph.co.uk drawing in more users worldwide.
The Sun Online held onto third spot with 1.9m UK unique users, a growth of 20% year on year.
It was followed by the Times Online with 1.8m UK unique users, also up 20% from April 2007.
The Daily Mail was the fifth most popular with 1.7m UK unique users, despite it experiencing the largest year-on-year growth -- a rise of 92%.
However, both the Guardian and Telegraph had the highest percentage of light visitors (users who spent less than 5 minutes on the site during April) with 83% and 81% respectively.
Only 6% of the Guardian's UK unique users and 7% of the Telegraph's UK unique users engaged with the website for more than 15 minutes during April.
Whereas 14% of the Sun's UK unique users spent more than 15 minutes on the website during April, followed by the Times with 13% and the Daily Mail with 12%.
Stephen Brooks, UK managing director of Nielsen Online, said: "Analysing the Telegraph's audience by heavy, medium and light visitors reveals their dramatic growth in popularity is concentrated around light users, which could be due to the site's improved visibility in search results.
"The Times, on the other hand, has experienced much less growth but this growth is mostly focused around heavy visitors.
"This encapsulates the 'reach vs engagement' conundrum that newspaper sites face -- is the best path to financial success attracting the most visitors or having a smaller core of more engaged users?"
The figures follow last week's announcement by the Joint Industry Committee for Web Standards, advisor to the ABC on its measurement methods, which revealed that it would undertake a review of the web measurement standards for the UK's national newspaper websites.
Rival publishers had raised concerns with Jicwebs following Telegraph.co.uk's dramatic rise in users over the past two months.
Telegraph.co.uk overtook Guardian.co.uk as leader of the national newspaper websites, according to the ABCe, after attracting a record 18.65m unique users during April, up by almost 10% from March.