Earlier I found two of these growing out of a strictly Geranium (Pelargonium) pot. Is it not an Escheveria? How this got there I will never know. The Escheveria is the opposite side of the garden and I haven't moved soils or plants.
Ah ha, Pete, I think you are correct. A big clump of Osteopernum grows less than a meter away and it had overtaken these pots a couple of years ago when I couldn't look after things. It is coming out of the pot bottom right corner (where there is a gap) and the Osteopernum is creeping out to the lounger in the background. Don't know why I didn't think of that! Thank you. I shall pull it up (there are two) and plant in the rockery down the bottom near the gate.