This must surely be the quintessential toadstool! Even if you have never seen one in the 'wild' you will have seen this fungus in children's books and cartoons; it is, of course, where fairies and other strange things live.
The Fly Agaric is quite unique in appearance being the only really red fungus, especially one with white spots on it. They are not white spots as such, but remnants of the outer casing that existed as the fruiting body emerged from the ground.This is quite common in the birch woods of Dorset as it has an affinity with birch. You can find it in September and October and possibly even in to November.