I believe this is an important tradition, since Belfast is one of the very few cities in the United Kingdom where its Lord Mayor is accorded the status and style of "Right Honourable".
This rank was conferred upon the Lord Mayor of Belfast by GEORGE V in March, 1923.
Normally nowadays the prefix indicates that a person is a privy counsellor; though in the case of lord mayors of London, Belfast, Cardiff, York etc it alludes to their rank as a baron.
The mayoral robe is probably made of black silk damask, trimmed with gold lace.
|The Rt Hon Michael Gove MP, Lord Chancellor, 2015-|
The Lord Chancellor wears similar official dress on ceremonial and state occasions.