[Excerpt - Article by C. Macoll Botley, lionandlamb.org, March 1966 - Linked above]
But I am indebted to Bro. Newton, Assistant Librarian at Grand Lodge, for the information that the ‘Lion’ also appeared on the Armourial Bearings of the Duke of Kent, whilst the ‘Lamb’ on those of the Duke of Sussex [Grand Masters of the 'Antients' and the 'Moderns' at the Union in 1813].
Thus the Name ‘Lion and Lamb’ was adopted by the lodge at the time of the formation of the United Grand Lodge, and it symbolises the merging of the ‘Antients’ represented by the ‘Lion’ with the ‘Moderns’ represented by the ‘Lamb’ of the duke of Sussex. There is also the Old Testament quotation, "The Lion and the Lamb shall lie down together".
The name was also adopted to commemorate the very noteworthy participation of the brethren of the Lodge in the negotiations culminating in the creation of the United Grand Lodge.
The ‘Lion’ is also a constant reminder of our roots in the Antient Grand Lodge, the ‘Atholl Masons’.
Fraternally, Philip Carter / Facebook / Great is Truth and mighty above all things (I Esdras 4:41)