Beware

This is Hemlock Water Dropwort.  Oenanthe crocata. One of the most poisonous of our wild plants. In fact every part of it is poisonous. It has been responsible for a number of deaths. Several of these have been tourists from Europe who have mistaken it for Wild Celery.
It prefers to grow alongside rivers and streams and in ditches.
Here it is growing alongside the River Kent.