Looks like orache. Certainly of that family, like fat hen. Chenopodiaciae is the genus in case it's not on your veg list, and you can look it up in a wild flower book.

Is that the same family as spinach and spinach beet, Worthy? Look rather like spinach flowers.

Closely related. I didn't think of spinach!

thought it looked a bit chard like

All similar things, Andy. Whichever it is, I would advise removing the flower heads as these will take energy away from the leaves, which is what you want. All of our spinach beet is bolting this year, I assume due to the heat.

I ate the flowerheads of some last night, (as a test). The oldest ones were a bit bitter, but the rest were quite tasty.

You still alive then, or is GoY now posting divine messages :-).
I supose that the flowers are edible but you are the first person I have heard of eating them, Worthy.