Sections of UK airspace will be opened on 20 April but the crucial area around London will stay closed at least until 13:00 local time.
Scottish airspace outside of the contaminated area will open at 07:00. Until then all UK airspace remains 'zero rated', says the Eurocontrol Central Flow Management Unit.
London's flight information region and upper information region will continue to be 'zero rated' at least until 13:00.
Northbound departures from the northern extremity of the London FIR, and outside of the contaminated area, will be allowed to operate with prior approval.