Can anyone tell me what this plant is please?

[neddle]

My parents have this mystery plant in their garden. It appeared last year, but they don't know what it is..
Any ideas?

I'd have a go, OP, but the pic's too dark to see!

Definitely need a better picture.

I agree it's too dark, but if you don't have another picture are there any other clues? Has it ever flowered?

Looks like Euphorbia lathyris, caper spurge. Also called mole plant, it was supposed to repel moles but I read that in fact it was used medicinally to try and treat/remove moles on the skin which is why that name became popular. I have it in my garden and I have moles both in the lawn and on my skin. The sap can be an irritant, as with any euphorbia. Seeds everywhere too but easy to pull out.

definitely caper spurge
lovely plant
leave it be
when the seed pods go they make a fab "crack"

Thanks for the info.
Is it safe to leave in their garden? They have a cat and I have 5 children aged 13 to 9 months.

yeah, I've always had them in my gardens with cats and kids and visiting kids