Victoria Beckham has said that despite her success she still has moments of self-doubt.

The mother-of-four, who celebrated her 40th birthday last week, has gone from Spice Girl to top fashion designer.

She told Mashable: "I think everybody has crazy moments of self-doubt and an element of that is probably quite important.

"There's nothing wrong with having a second little person sitting on your shoulder, making sure that you are remaining humble and appreciative of everything that you have.

"But you should definitely not waste too much time being negative in any way. It's about positive thinking, positive energy, and fighting if you need to fight."

She said of her new career: "I didn't go into this to prove anything to anybody other than myself."