I expect most of us are familiar with snap-dragons as we called them when I was a child. If you press the sides of the flower near the base the mouth opens! Common toadflax (Linaria vulgaris) is the natural version of the antirrhinum we used to grow in the garden.
As the name implies, it is fairly common and thrives on calcareous soils and hence does well in parts of Dorset. It flowers from July right through until October and you can find in waste areas, on grassland, in hedgerows, along roadside verges and railway tracks, anywhere where the competition from other plants is not too great.
I have also heard this called Tom Thumb and eggs and bacon but I think both of these country names really apply to bird's-foot trefoil. There are numerous other colloquial names for it and Wikipedia has quite a long list if you are really interested! It is also an extensively used plant in herbal medicine curing alomost as many ailments as it has names ...
Common toadflax is a lovely flower; it is well worth taking a closer look if you find it.Common Toadeflax: the snap-dragon