Cheryl Tweedy, 19, from Newcastle upon Tyne, is the singer with the all-girl group.

She was arrested after 39-year-old law student Sophie Amogbokpa was allegedly punched in the eye in the toilets of a Surrey nightclub known as The Drink.

Ms Tweedy was released on police bail after being held for 10 hours.

Eye injury

Ms Amogbokpa was taken to the Royal Surrey Hospital for treatment to an eye injury.

A Surrey Police spokeswoman said: "A 19-year-old woman was arrested in connection with an allegation of assault in the early hours of Saturday morning.

"She has now been released on police bail pending further inquiries."

Ms Tweedy was one of the winners of the ITV show Popstars: The Rivals.

The all-female group's Sound Of The Underground became the 50th Christmas number one single - beating another group formed by ITV1's Popstars: The Rivals, boy band One True Voice.