Diana Vickers looks set for number one with her debut single, Once.

The 18-year-old X Factor star from Huncoat is already top in the iTunes download chart.

And she is being tipped to follow that up by leading the official top 40 this Sunday, which combines singles and download sales, after the release of the CD version today.

Diana Vickers was described as the odds-on favourite for the spot by bookmakers Betfred.

A spokesman said the betting opened up at 12-1 and she has been heavily backed at 1-3. He said: “After reaching number one in the iTunes chart, it looks virtually certain she will be at number one on Sunday.”

Chart-topping success would confirm Diana's remarkable rise since reaching semi-final of the X Factor in 2008.

She received rave reviews for her performance in a West End production of Little Voice, and has since been working on her album Tainted Cherry Tree, which is due to be released next month.

The video for Once has been played regularly on MTV and other music channels, while mainstream radio stations also have it on their playlist.

In addition, Diana is on a whirlwing publicity tour this week to promote her single. She will be on Channel Four's T4, ITV's Loose Women and Radio One's Live Lounge session on Thursday.

At the weekend she performed at London's G.A.Y. night club.

And all her hard work is paying off with once already leading the iTunes chart, which is calculated on the number of times the song has been downloaded by users of the popular site.

Rob Brown, manager of HMV in Blackburn, which sold a handful of copies of the CD single yesterday, said: "These days download sales are hugely important, accounting for about 90 per cent of all sales.

“If she’s gone number one on downloads and can hold on all week, the chances are, she’ll be the official number one at the weekend.”

East Lancashire people said her success was great for the area.

Pete Eastwood, 46, of Pleckgate, Blackburn, said he would be buying the single. He said: “As much as X Factor wasn’t really my bag, she’s a local girl with talent, so why not support her?

“She gets loads of stick, but I was surprised at the quality of the songs she’s done."

Nicola Young, 24, a part-time student of Audley, Blackburn, said: “It’s a while ago now that Diana was on the X Factor and I think that people are now more interested in Joe McElderry.

“It’s good that someone from around here is doing well, but I won’t be buying it.”

Anne Patefield, vice principal of Westholme School, which Diana attended from the age of four to 16, said: "We always knew that she was a star. It’s great to see that others now see that to