Which is a legality; I'm much more interested in the practicalities of not digging a hole in a field.
I don't recall the specific RT - it wasn't directed at me and I was busy, but the PA28 pilot certainly believed that he'd been cleared to transit the overhead at 2000ft on his lower QNH.
I was in an active circuit, and there are rules about fitting in with that - by telling him that he could route through the overhead, arguably the controller was telling the PA28 pilot that he need not fit in with the circuit. So he didn't - flew where he believed he had been "cleared", and the result thankfully wasn't nasty, but could have been with things just a few seconds and 100ft different (and poorer lookout than mine thankfully was): that interests me a lot !
G