The umbellifereae (or carrot) family of plants present many difficulties for the casual observer, even those with some basic botanical knowledge. As always, my advice for what it is worth, is to try get to know them one at a time and the most common ones first. That way you know when you are looking at something different.
One of the ways of separating them is by order of flowering, cow parsley (Anthriscus sylvestris) comes first, followed by hogweed, then rough chervil, upright hedge-parsley and finally wild angelica. This is a simplistic guide and applies to only the common hedgerow 'carrots'. The cow parsley starts flowering in April (earlier in sheltered spots in warmer years) and goes on until June. It can be found on just about every Dorset roadside and woodland edge except where the soil is poor and not very deep.
I have to say I am not a fan of cow parsley! It thrives at the expense of other plants. We have become very 'tidy' in our roadside verge management. The herbage is cut down just as it is starting to get going and the strongest, quickest to recover is cow parsley which then blots out everything else. This practice over thirty or more years has led to cow parsley and its relatives taking over from all but the strongest of its competitors, often campion and comfrey.
In its defence, these plants are very popular with insects and I love to walk along a quiet road or lane looking at the flower heads, you find all sorts of bees, flies and bugs!