Hypericum hidcote is what the flower looks like. There are a number of hypericum varieties though, so can't be 100℅ without seeing the whole plant, usually gets about 6 or 7 feet high and wide if not pruned yearly.

it is indeed Hypericum one of its common names is Rose of Sharon, another is St John's wort. Can be a lovely plant though some people find they can become a bit of a thug.