Are the earths provided by steel conduit?
Into a 16mm shallow backbox?
I thought it looked like a 25mm
It looks like singles have been used which does suggest round conduit.
Perhaps old half inch conduit has been used. I believe a special bush could be used to couple up to plaster depth boxes.
If there is no earth present at all, and plastic switches are used, are we back to that old, old chestnut of using nylon screws?