in fact i could be more like 20 weeks 
(long story to do with not being sure of my dates)
but anyway, got the letter today with my scan date and based on the LATEST possible time i conceived, i will be at least 16 weeks
i think its appalling. i rang and explained the situation but they will not cannot give me an earlier one
gutted. we have no money for a private one otherwise i would book one immediately