Depends on a few things. firstly on the airfield and type of ATSU, lets assume this case it´s Gloster approach as thats my home field!
Then if you´ve remained on the Freaquency after departure and just mooched about doing some local flying. In this case the correct call as per my training is
me: Glos app G-xxxx
G-xxx, App pass msg,
App, G-xxxx is overhead x, alt y, QNH zzzz, request rejoin (and include ATIS where appropriate)
If either returning to home after a freaquency change or to a different field, then the procedure should be the full report, i.e.
Gxxx is a (type) from airfield a to airfield airfield b currently overhead X at altitude Y, QNH Z request joining instructions