Might have something to do with the 'friendly' disputes between England and Scotland who are represented by the Lion for England and the Unicorn for Scotland.
There is a Nursery Rhyme which goes .... The Lion & the Unicorn were fighting for the Crown, the Lion beat the Unicorn all around the town. A Scottish King, James VI had become James I of the whole country.
Perhaps Milner felt that is was provocative to award the crown to the Lion.
Attachment 22176