Most Hogweed  (Heracleum sphondylium)  flowers are white although some have a pinkish tinge and occasionally entirely purple like this.  A white one is in the background.  The flowers are arranged in umbels which can be up to 25 cms in size and blooms between May and August in hedgerows, on verges and wasteland and it is rated in the top 10 for most nectar production in a survey of UK plants so is useful for insects pollinating crops.  In winter the hollow stems are sometimes used by nesting solitary bees  It used to be given to pigs hence its name and is not dangerous like the introduced Giant Hogweed.