A flow stop valve positionable in a downhole tubular, and a method. The flow stop valve is in a closed position when a pressure difference between fluid outside the downhole tubular and inside the downhole tubular at the flow stop valve is between a threshold value, thereby preventing flow through the downhole tubular. The flow stop valve is in an open position when the pressure difference between fluid outside the downhole tubular and inside the downhole tubular at the flow stop valve is above a threshold value, thereby permitting flow through the downhole tubular.