It is a Gatekeeper (Pyronia tithonus) a butterfly that is very successful in the southern half of England. In recent years it has been gradually extending its range northwards. It is sometimes called the Hedge Brown because it favours shrubs and hedgerows. It lives in colonies of variable size and doesn't stray far from its community. It likes to rest with wings outspread in the sun.
Gatekeepers start to fly in mid-July with a peak of butterflies at the beginning of August. The flight period ends with the end of the month.
This particular individual is a female, already looking a little ragged on the hind wings. Males have a dark band of scales on the forewing - this is called the 'sex brand'. Although they are common and widespread they are vulnerable to intensive agricultural practices and removal of hedgerows.
Candytuft (Iberis umbellata) is a member of the Brassicaceae family, related to mustard. The name derives from Candia, the former name of Iraklion in Crete.