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)
Thankfully we never hear " If you read this transmission squawk ident" then
However, Both the ICAO R/T manual and the local UK CAP 413 require either a readback or an acknowledgement of an instruction to squawk ident.
Regards,
DFC