and it is a requirement that Class D VFR flights are in ATC contact
True, but it's possible to create exceptions. For example, the Manchester Low Level Route is Class D, but no contact with ATC is required to use it as long as you comply with certain rules (clear of cloud, in sight of surface, max altitude 1250', min viz 4km, and either transitting north/south through the zone or to/from an airfield in the zone).
FFF
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