in no circumstances
Never; in no case or situation; irrespective of events or conditions. In no circumstances are you allowed to drive home after you've had more than one drink! I'm sorry for my sudden resignation, but in no circumstances will I work for some sexist manager like him.
in/under no circumstances
used to emphasize that something should never happen or be allowed: Under no circumstances should you lend Paul any money.Don’t open the door to strangers in any circumstances.