Actually, when off shore pirate radio closed down, at least one station cotinued, for a while.
Stations also popped up in the big cities. London had many, of course, including Radio Jackie which continues in some form even now.
We live close to a tall tower block. For a period of time, pirates operated using an antenna on the roof. It interfered badly with our tv.
Nowadays, of couse, anyone can set up a station. The Internet is your friend.