Garden City principles as first implemented at Letchworth GC include a surrounding belt of countryside to prevent urban sprawl and coalescence. This principle is re-inforced in Section 9 of the NPPF. Development at site HT1 will diminish the extent of the green belt around Letchworth (as noted in the Policy SP17) .The green belt is not only part of the setting of the heritage asset that is our first garden city but also part of that heritage asset. Development here will cause harm to the significance of Letchworth and its garden city status.