Transfer diamonds in royal house (4,4)
I believe the answer is:
hand over
'transfer' is the definition.
(I've seen this before)
'diamonds in royal house' is the wordplay.
'diamonds' becomes 'd' (abbreviation in bridge say).
'in' indicates putting letters inside.
'royal house' becomes 'Hanover' (Hanover is an example).
'd' going inside 'hanover' is 'HAND OVER'.
(Other definitions for hand over that I've seen before include "Pass across; surrender" , "Yield possession of in overhand way" , "Deliver into control of another - in manual way?" , "Present or give to another person - manually?" , "Transfer" .)