Just nitpicking
British registered craft fly one of three types of Ensign (basically a nautical type of flag) depending on their classification.
The White Ensign
Flown by the following
Warships of the Royal Navy
Private craft of the Royal Family along with the relevant royal standard).
The Royal Yacht Squadron
The Blue Ensign
Flown by the following
All Unarmed ships of the Royal Navy
All private vessels owned by members and ex members of
Her Majesties Armed Forces.
The Red Ensign
Flown by the following
All British privately registered vessels which dont fall into the above categories.