UK civil controllers can't use squawk ident to identify a 7000 and I suspect a lot wouldn't use it for any of the other non-discrete codes. You can be identified over a VRP at or below 3000 feet though, so it might have been that if you were near one but there are many other possibilities too.
Ah I see...I was overhead a VRP so perhaps that is the case.
Im not criticising the ATCO here btw, I was just looking for someone more informed than myself to explain the limitations that radar controllers have in identifying aircraft.
Cheers