These tall plants are Hemlock (Conium maculatum) I believe. As mentioned in my last entry the Umbellifer family includes some very toxic species, Hemlock among them. All parts of the plant are poisonous if consumed and can be a severe irritant to skin/flesh/eyes if handled. 

  

 I heard on the radio recently that Hemlock has grown high and mighty this year as a result of the wet weather (so have a lot of plants). A row of them lined a footpath I walked along last week and they were a good eight or nine feet in height.

 The purple specks and blotches on the stems are characteristic of C. maculatum.