More than 150,000 copies of Coldplay's new album X&Y were sold on its first day of release.
Coldplay will headline the Glastonbury Festival on 25 June
Music experts expect that up to 500,000 copies of the album will be sold this week, sending it to number one.
X&Y could have the UK's highest first week sales since Be Here Now by Oasis, which sold almost 700,000 copies eight years ago.
Shop chain HMV said many of its stores opened early on Monday to find fans queuing outside to buy X&Y.
Spokesman Gennaro Castaldo said sales of the album should comfortably exceed the 400,000 mark.
"It's no surprise that Coldplay sold so many albums yesterday - as much as the rest of the top 20 combined," he said.
"Demand has been building for some time and there was a real buzz of excitement in all our stores around the country.
"There's only a handful of artists that have this kind of effect, and Coldplay are one of them.
"We haven't seen anything like this since Be Here Now.
"It's fair to say that we're already looking at the biggest album of the year by far."
The rapid sales come despite the album being illegally put on the internet a week before its US and UK release.
Coldplay were beaten to the number one spot in the singles charts last month by the Crazy Frog.
Hundreds of fans also queued to get tickets for a one-off Coldplay gig in London on Monday night to mark the launch of X&Y.
Coldplay kicked off the show at the 1,200 capacity Koko in Camden with Square One from the new album, followed by old favourites Politik and Clocks.
The band are also due play a number of big UK outdoor shows this summer as part of their world tour, which includes an extensive list of US dates.