whats is this plant please

This looks like Nightshade (black)

That's what I thought - whatever you do, don't eat it.

it certainly looks like a nightshade, there are quite a few types best destroyed to be on the safe side

I have looked it up. I wouldn't rule out the possibility of Deadly Nightshade, but would agree most likely Black Nightshade. Ingestion causes vomiting, diarrhoea, colic, headache, respiratory depression, clammy skin, fever. Rarely death. You'd be better off growing a begonia instead.

thanks for the answer I will destroyed the plant.
the one plant came in a packet of petunia seeds

Funnily enough, there is a form of Black Nightshade called Garden Huckleberry that is quite edible though unless you know exactly the sub-species, bin it!

Here is a link to the edible one. Incidentally, the last sentence in the text of the link (below) is incorrect. It states that the plant is an edible form of Deadly Nightshade which though related, it is most certainly not. Deadly Nightshade belongs to the genus Atropa, this is a Solanum.

http://www.tradewindsfruit.com/garden_huckleberry.htm