Brits here say it's illegal to fly the Blue Ensign unless you are a full-paid naval officer...etc.
All yachts have to fly a Red Duster or facing a hafty 5,000 pound fine and maybe with boat confiscated.
Of course, you have to be a "British Subject" first before you are allowed to fly either one.
Then, I found this on the Web: www.crwflags.com:
Even some Yacht clubs are allowed to use the plain blue ensign:
* Royal Albert Yacht Club
* Royal Cinque Ports Yacht Club
* Royal Cruising Club
* Royal Dorset Yacht Club
What about Australia and New Zealand? I notice most Aussies and Kiwis fly their national blue ensigns.