Had a revamp of the garden and patio. Now want to build a wall to support a raised border. The wall needs to be no higher than half a meter and intend to build it out of a load of sandstone rocks I have.

Do the masses think for this height of wall, I need to go for a full blown footing of 300mm wide by 150mm deep or think this is a bit of overkill?

That’s hardly “full blown”. It’s adequate if the ground it founds on also is…

yeah, no foundation required for 0.50m high wall. Probably worth a bit of mortar/cement in the wall gaps to stop it beng pushed forward.