/usr/share/myspell/dicts/en_GB.dic is in myspell-en-gb 1:4.2.1-0ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/myspell/dicts/../../hunspell/en_GB.dic
/usr/share/myspell/dicts/../../hunspell/en_GB.dic