Flag flying protocol for vessels during the period of National Mourning

From as soon as possible until 8.00am on Tuesday 20 September, all official flags flown on British marine vessels, including the Union Flag, should be half-masted. 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. Other official flags scheduled to be flown can be flown as normal, but at half-mast.

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. 

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. 

If your flag is on a pole that is more than 45° from the vertical, flags cannot be flown at half-mast and therefore should not be flown at all.

The Union Flag must also 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. 

College of Arms guidance can be found here and more information about the flag flying protocol issued by the flags and heraldry committee is available here.