One of the first things I spotted in my new garden (in Kent, nearish to London) was a datura/jimsonweed/thornapple aka whatever else. I spotted its leaves and they triggered some memory or other. I thought at first it was a young giant hogweed with the very indented leaves, but then realised. I looked it up on the Royal Horticultural Society website, and, as a consequence, when i had photographed the flower and the fruit, dug it up with rubber gloves on (the active chemical can be absorbed through the skin) put it in a bin bag, every part, and took it to the local dump where household rubbish goes to be incinerated. With the gloves. Apparently there are some parts which it is safe to compost, but I was taking no chances.
No idea where it came from, but interesting. When I was a child in Folkeston, there was a picture outside the police station (along with one of Colorado Beetle) with warnings about it being around in a local nature area. Where I never saw it, but wanted to.