Cabinet Office
Following the death of Her Majesty The Queen, all official flags, including the Union Flag, should be half-masted from as soon as possible today until 08.00 the day following The Queens State Funeral. Flags may be flown overnight during this period but should remain at half-mast.
Official flags in this instance are defined as national flags of the home nations, Crown Dependencies and Overseas Territories, Ensigns and Ships colours.
Any non-official flags flying or due to be flown, such as the Rainbow Flag or the Armed Forces Day Flag, should be taken down and replaced with a Union Flag at half-mast. Other official flags scheduled to be flown can be flown as normal, but at half-mast.
Half-mast means the flag is flown a third of the way down the flagpole from the top, with at least the height of the flag between the top of the flag and the top of the flagpole.
On poles that are more than 45 from the vertical, flags cannot be flown at half-mast and should not be flown at all.
The Union Flag must be flown the correct way up - in the half of the flag nearest the flagpole, the wider diagonal white stripe must be above the red diagonal stripe. Please see the College of Arms website
Royal Standard
The Royal Standard is never flown at half-mast even after the death of a monarch, as there is always a Sovereign on the throne and it would therefore be inappropriate for it to fly at half-mast. The Union Flag will be flown at half mast on all Royal Residences.
Exceptions for half-masting during this period of mourning
The only exception to half-masting during this period of mourning is on the day of the Accession Council on 10 September when His Majesty The King is formally proclaimed. The Union Flag and all other official flags should be raised to full mast between the hours of 09:00 and 10:30 and remain at full mast until 13:00 the following day, at which time the Union and official flags should re