If I do a steep climb I find that my rear mech cage rubs the spokes :-O

It seems to do it intermittently, and the level of rubbing seems linked to how much power I try and do the climb with. I assume, therefore, that it must be the rear wheel flexing as the frame is an Argon 18 Galium Pro so I doubt it’s the stay flexing?

Be good to find a solution to that problem.

Agreed. I don’t think it’s the mech hanger being bent or the gears adjusted incorrectly as the shifting is ok.

When you are in low gear how much distance should there be between the bottom of the mech cage and the spoke.

If I know that I can conclude whether it is the rear mech cage / mech alignment that is incorrect?

Whatever it is sort it out ASAP. I have seen too many rear mechs get caught in the spokes and ripped off. In all instances the warning signs were the cage tickling the spokes going up hill. Might be worth blocking off the lowest gear via the limit screw until this is sorted.

It will be the top of the cage where the rubbing occurs.

Good advice above. If your shifting is still accurate then the issue is likely to be with the wheel.
Spoke tension, bearings, axle, rim and hub integrity.

“neilwheel” – Just checked, and yes it is the top of the cage where it is rubbing as I can see the paint has rubbed off that part of the mech

Good idea about setting the limiting screw until I get it resolved.

I will drop the wheel down to the LBS to get them to check the spoke tension …