A Wasp Spider (Argiope bruennichi). These are spreading northwards in the UK, but came from Europe.
I first saw one a couple of years ago in the meadow near the house and watched it all summer. This one’s in the garden so I can see it whenever I go outside. The strange zig zag on the web is called a ‘stabilimentum’ and it’s unclear what it’s purpose is – but maybe it’s to ‘stabilise’ the web!
Anyway…I’ve found out more. The spider is a ‘she’. The male is tiny and boringly brown in comparison, and often doesn’t live long after mating. (Euphemism there, as the female kills him.)
The huge, basket/seed pod-like thing behind her is her egg sac. Carefully spun and then filled with eggs and then sealed. And guarded now in a new web.
When the proper cold weather arrives apparently she will die. The babies will overwinter in the sac and emerge in the Spring…