Whilst this could appear to be a close up picture of meadowsweet it is actually a totally different species; dropwort (Filipendula vulgaris). As dropwort and meadowsweet look so alike this is a case of using other criteria to make an identification. Whilst meadowsweet is a plant of wet (or at least damp) ground dropwort thrives on dry chalk grassland. They are such similar plants but they have totally different requirements in terms of habitat. If you want to be totally sure which of the two species you have found then look at the leaves, they are very different. Meadowsweet has bold rose-like leaves whereas those of dropwort are much more akin to ferns.
Surprisingly, perhaps, It is a member of the rose family. It is locally common but not widespread in Dorset and is always a nice find in June through to August.
Wikipedia tells us that dropwort flowers have been used in Austrian herbal medicine as a cure for rheumatism, gout, infections and fever. It also tells us that the name dropwort comes from the tubers that hang like drops from the root.Dropwort: a rose by any other name