The United States has a status of "US Person". Please create the new status of "UK Person" for those who already qualify for British citizenship but who cannot obtain it because their country of origin prohibits multiple nationalities. A "UK Person" would enjoy all the rights of British citizenship.
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Many non-British UK residents qualify for British citizenship, but their existing nationality prohibits multiple nationalities. Please give them the option of applying instead for "UK Person" status, which would give all the rights of British citizenship, but without infringing laws prohibiting multiple nationalities in their country of origin. A "UK Person" would have the same voting rights as British citizens and could perhaps be issued with a new "UK Person" non-citizenship British passport.