Tulisa Contostavlos was not over the drinking limit

Singer and the former "X Factor" judge Tulisa Contostavlos, who was arrested on suspicion of drunk driving earlier this week, is "absolutely convinced" that she was not over the limit.

"Tulisa had just one drink, a vodka, and it was only a few minutes earlier - but she needed to pop to the shops for a few bits. She was careful not to have another drink and jumped into the car. By the time she was breath analysed it was around 20 minutes later and she was confident that she would pass the test," mirror.co.uk quoted a source as saying.

Contostavlos was arrested allegedly after she crashed her Ferrari in Southgate, North London, on Thursday night.

"But the machine flickered right on the brink before coming back - positive. At the police station she gave a second sample after insisting she wasn't over the limit. She is completely convinced she hadn't drunk too much to drive. She believes the breath test was affected by the fact that she had the vodka such a short time before - but is sure the quantity she had was below the legal limit," the source added.