Thank you Sama!* I would love to come to England.* My father was born in London.* He always told me it was in a hospital either around the corner from Big Ben or could be seen from Big Ben, but that was in 1904!* I doubt the hospital would still be there.* Besides, he left when he was 4 years old and wouldn't remember it.
I still don't know what you saw, but I suspect it was the larval stage of some pest.* Maybe diatomaceous earth would work.* It would have to be the food grade, not the stuff you put in swimming pools.* If you do use it, don't breathe in the dust as it's bad for the lungs.* Otherwise it's harmless to humans.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.