Originally Posted by ATC: "(callsign) squawk ident."[/I
Pilot: SILENCE 
What do you expect?......perfectly acceptable!!!!!!
[/quote]
LIKLIK
I can't copy the ref. for this but CAP493 appendix E p9 specifies:-
Pilot readback of RTF messages
SSR operating instructions
Controllers are to prompt a pilot if a readback is not immediately forthcoming
Also in CAP 413 RT Manual (for pilots and ATC)