A UK flagged vessel should fly the Red Ensign during daylight. It must be worn when entering a foreign port. They are not worn while racing. The ensign should be flown from the stern of the vessel.

Sewn Flag - Premium quality sewn national flags are manufactured at it’s premises in the United Kingdom. These flags are manufactured to the highest standards using a woven polyester fabric specifically designed for the flag industry and the latest synthetic machining threads. Woven polyester Flag fully sewn. Finished with hems heading rope and toggle

The size of the flag should look appropriate for the boat. An approximate guide often used is 1 inch per foot of vessel or follow the guide below:

Approx sizing, a guideline, not exact