As above, I52 is under the parcel shelf and accessed via the boot.
There's a load of relays there on a P1 but fewer on P2 ( this is my P1, yours will be different ).
It's easy to identify on a P1 as the relay base is green. According to the manual, this useful colour coding was discontinued with the P2 and the relay base is black ( as is the fuel flap relay ). You'd therefore need to identify it by the wires :
Yellow : Relay coil supply from N82 Services Unit
Black : relay coil earth
Red ( thick ) : +12v
Green ( thick ) : to the opening solenoid.
Is it possible that my car has some unique wiring / set up? I relayed PKR's point re yellow / red-yellow wires and the guy reckoned that's what he expected to see on mine, but didn't.
I could envision undocumented wire colour changes ( there are parts of my P1 that do not match the manual ) but the basic operation will not have changed.
Ultimately, there are only three wires going to the glovebox and a quick continuity test on the switch would have shown which two wires it switches. As one has to be earth ( otherwise the glovebox light wouldn't work! ) the other one has to be signalled low when the switch is pressed.
Did he take the glovebox out? I suppose he could have traced the yellow-red to the N82 and felt he'd got a bit out of his depth.
You could unplug the light/switch unit in the glovebox and have a look at the wires yourself. The 3 wires should be Black ( earth ), Yellow-Black ( sidelights for glovebox light supply ) and Yellow-Red.