Prydz looks to get physical in bid to overhaul Perry's four-week reign.

I Kissed A Girl by Katy Perry continues at number one, securing its fourth week at the chart summit on sales of 40,587 downloads. It is the sixth song to spend four or more weeks at number one so far this year but the first by an American female soloist to endure that long since Cher's Believe locked in to the top slot for seven weeks a decade ago.

I Kissed A Girl is finally released physically today (Monday) - but so is closest rival Eric Prydz's Pjanoo. Perry's boost will likely be small, as I Kissed A Girl is available on just a two-track CD single, whereas Pjanoo is due on six-track CD, two-track CD and four-track 12- inch, and will doubtless get a big push from label Data's parent company Ministry Of Sound, who will be eager for the label's 200th release to get to number one.

After debuting last week at number 10 to become their biggest hit, Biffy Clyro's Mountains makes a further, significant move upwards, following its physical release. It sold 20,416 copies last week, boosted by the release of two seven-inch picture discs and a CD. It is that 21st-century rarity of a "non album single" but its success has raised the band's profile and provides a lift to their most recent album, Puzzle. The album reached number two in June 2007 - it was kept off the top by Rihanna's Good Girl Gone Bad - but has improved 167-140- 108-76 in the last three ...