Unique, like an empty House of Lords? (8)
I believe the answer is:
peerless
I believe this clue is a double definition.
'unique' is the first definition.
(I've seen this in another clue)
'like an empty house of lords?' is the second definition.
(members of the House of Lords are peers)
(Other definitions for peerless that I've seen before include "Without equal or match" , "No Iolanthe performance could be so" , "Without equal, being without a lord?" , "Without equal or lacking lords" , "Excellent" .)