your plant is indeed a dock - Rumex crispus the Curled Dock. Its called that because the edges of the rather pointed leaves are wavy. It's a good time of year to identify docks as they are most easily distinguished by the characters of the fruits. The shape of the valves - the 3 of which hide the nutlet inside - is diagnostic. In this case the rather heart shape with only very limited development of marginal teeth and an obvious tubercle (the blob) on each valve tells us its Rumex crispus. It is one of the 3 commonest Docks in the country growing in a wide variety of habitats from wet to dry and the seashore to upland meadows.