Esspee: from a health point of view in the UK, there is no legal 'next of kin'. You can name who you like (I think some US States have rules about it, also it's a 'plot device' in some dramas).
However, if it comes to serious decisions, it is advisable to have a health & welfare power of attorney in place. That applies even if you are married.
Angela Rayner lashes out and calls Sunak “pint sized loser”.