“Mummy’s doing a big test” was the method she explained it to her sons. A statement instructive that upstart is more acutely aware than the woman herself that Victoria Beckham: fashion designer is a job title under constant inspection. But today as Beckham presented her fourth dress gathering during New York Fashion Week, the designer proved that the phenomenal success her own label has enjoyed so far is neither fluke nor whim, and that she is in the fashion business for the extended game.

In just four seasons Beckham has developed a strapping signature look – slim elegant lines, a controlled sexiness, and a eager attention to detail whether it be an internal corset or a rose-gold zip snaking the length of a dress.

Seated in the front row of her tiny salon-style show, Beckham talked the audience through the collection using a simple technical vocabulary that Central Saint Martins lecturer would be proud of. She explained that the group was “an exercise in control: working with structure and drapery”. She claimed to have been prejudiced by a “1940s femme fatale and a Dick Tracy cartoon colour palette” – meaning blood scarlet sapphire, emerald and graphite. Best was a loose sweater-meets-couture dress that Beckham herself had chosen to wear. Oscar-ready gowns worn with sunglasses finished the collection.

So victorious is the Beckham line that despite its heavy price tags it has sold out during the worst of the recession. Insiders guess the Victoria Beckham dress, denim and sunglasses business will be worth $7.5m (£4.7m) in sales this year.

Following the show Beckham said “the dream” was to open a shop in five years’ time and joked that her nine-year-old son Romeo wanted to take over the brand one day. Given Beckham’s natural design skills and steely determination, it is likely that there will be a successful label for him to inherit.