nosy parker 
noun British informal
An overly inquisitive person.A nation of nosy parkers, we just can't resist the chance to see what became of the twit we sat next to in maths, or if we've finally managed to outdo little miss marvellously witty, beautiful, intelligent, can-do-no-wrong....
- Flesh Sunday's narrator is a nosy parker who mistakes a murderer for a fellow peeping tom.
- All local budding Sherlock Holmes, Agatha Christies and other nosy parkers were running around last weekend trying to figure out what happened Friday Night at Bowmore Point.
Origin
Early 20th century: from the postcard caption ‘The Adventures of Nosey Parker’, referring to a peeping Tom in Hyde Park.