It’s been out of the ground for a couple of years. I'll be fitting it with new washing cord soon. Doing a quick Google, it would appear this style of ground attachment is called a ‘soil spear’. I’m presuming this type gets malleted into the lawn? Other types appear to use something called ‘postcrete’, but appear to be simple tubes. Plan is to soak the spot of lawn with water, so it’s easier to knock it in. Now how to make sure the soil spear goes into the lawn dead vertical? Any techniques? I’m guessed just one mallet whack at a time, following each whack with the spirit level?
FWIW, here's what I did. Cut out about a foot square of lawn, neatly so you can re lay it later. Dig a hole deep enough to take the spear and pour in a small bag of postcrete. Put a broom handle or similary long pole in to the hole in the metal spear and place it (like a flag pole) centrally in to the postcrete. The pole should be long enough to make establishling true vertical much easier with a level. Three or four temporary 'legs' attached and splayed out around the the pole will help brace the pole in to the lawn to keep it in the vertical position long enough for the 'crete to harden. You have time to tweak vertical correctness before the 'crete hardens. The top of the 'crete should sit below your turf level so that when you relay the turf patch the grass blades are flush with the rest of the lawn but the spear hole should be visible. Not so much it will knacker your mower blade though!
Put something in the soil spear, e.g. a piece of batten, and whack that in, taking the "spear" with it. It will be much easier to heep the thing vertical then, and yes, use a spirit level, bum plob or W.H.Y.