It seemed like a match made in fashion heaven, Sex in the City style icon Sarah Jessica Parker and Halston Heritage, the younger sister of the Halston brand, synonymous with Studio 54 and glamorous seventies style. But is seems that SJP and Halston Heritage have parted company after just 18 months. This seems such a shame. I don’t know if Sarah Jessica Parker ever actually designed anything, or whether she really sat on the floor sewing sequins on hemlines, as she once said in an interview, SJP became the person who embodied the revitalised Halston – glamorous, ambitious and super smart. SJP was a fab brand ambassador for Halston Heritage,…