The Guardian's audience grew by 11.9% in June, which was also up by 41% year on year.
Telegraph.co.uk, which relaunched this week, climbed back to second spot with a 6.57% month-on-month increase to 19.71m unique users. This figure is up by a massive 179.5% year on year.
However, the Telegraph has a considerably smaller percentage of UK users than Guardian.co.uk. About 6.47m of the Telegraph's users come from the UK, which is roughly 33%.
Mail Online suffered a poor month in June, slumping from top spot into third position.
The Mail's network of sites, which includes the combination of Dailymail.co.uk and MailonSunday.co.uk, slid 14.41% month on month to 16.02m. However, this figure is still up by about 69% year on year.
The site's UK users reached 4.99m, which is 31% of the total unique users.
Times Online meanwhile remains in fourth place. Its unique users climbed 3.1% during June to hit a record 16.37m, which is up 69.7% year on year.
Just over a third (35%) or 5.73m of the Times Online's users were based in the UK
Similar to Times Online, it also attracted 35% of its users from the UK.
The Independent.co.uk, which published its first ABCe last month, grew its audience by 10.44% to 7.22m unique users. No data was available regarding its percentage of UK users.
The network drew an impressive 56% or 3.04m of its users from the UK.