It's a white variation of Borage. There's also Feverfew in the picture. Did you ever sow some mixed herb seeds?

re sow mixed seeds, no. So its borage. Flowers and leaves are edible and medicinal, correct?

Edible, yes. Medicinal, perhaps, but I would not start self treating with it.

I personally find their flowers so scratchy with those stiff or even stinging hair, it makes mixed salads kind of uncomfortable

the white version keeps popping up, a neighbour in our alottment has those as well

The only real use I've come across is to float the flowers in a Pimm's. As you say, I wouldn't want to eat them or the foliage.