Tulisa Contostavlos says Little Mix's debut single is "a formality".

The N-Dubz singer mentored the group - who saw their cover of Damian Rice's 'Cannonball' reach number one in the UK singles chart yesterday (17.12.11) - to victory on 'The X Factor' and thinks they can go on to establish their own identity now they have released their first song.

If I'm being honest the debut single 'Cannonball' is more of a formality for them. The real fun will begin when they get in the studio and find their identity. That's when they're going to start the ball rolling.

She told the Daily Star newspaper: "If I'm being honest the debut single 'Cannonball' is more of a formality for them. The real fun will begin when they get in the studio and find their identity. That's when they're going to start the ball rolling."

However, Tulisa believed the group - Perrie Edwards, Jade Thirlwall, Jesy Nelson and Leigh-Anne Pinnock - - will go on to great things.

She said: "I do believe they are going to be the biggest girl band we've had for years."

Show chief Simon Cowell is thrilled by the success of Little Mix's single, which has sold over 210,000 copies since its release last week.

He said: "I'm absolutely thrilled. I think they have something really special."

While they are currently at number one, Little Mix are expected to lose the top slot on Christmas Day (25.12.11) to the Military Wives choir.