No - P-E-R , the Union Jack is the national flag of Great Britain (the poor Welsh don't even show in it!). For the Royal Navy the aft flag is the White Ensign, the Blue Ensign for naval auxiliary vessels and the Red Ensign for civilian vessels. The bow flag (jack staff) whilst moored is the Union Jack. P.S. this is not a complete explanation of British flagging. (eg a member of the Royal Yacht Squadron is permitted to fly the White Ensign)
Dragon tombs are to be found in Never, Never Land (current president Peter Pan) - their flag is yet to be designed, let alone published