An influencer is warning other women shopping in London’s West End “to beware” after CCTV caught the moment her new £10,000 Birkin bag was stolen as she tried on clothes at a boutique.Model Janice Joostema, who boasts 1.2million followers on Instagram, said it had been “gut-wrenching” to watch a female thief swipe the item while she got undressed in a VIP changing room at Manière De Voir on Oxford Street.