There used to be night flights into LHR, not many but some, not sure if they were all stopped. Also some early landings for LH were allowed. Dunno if that has changed since.
All of Europes flights have been totally messed up by bad weather for the last week, so it wouldnt be any surprise if some airlines pushed the curfew envelope to get already much delayed aircraft re-positioned, and LHR let it ride needing the aircraft in position next day to start clearing delayed pax...