My view is the article you linked provides the answer, there is no transit route, you enter the uk then depart again

If you arrive at London Stansted on an international flight you will need to pass through passport control/immigration, whether your connecting flight is domestic or international. You will therefore need the correct documentation for entry into Britain. If you are connecting from a UK flight to an international flight you will need to pass through special immigration control points where you may be asked to show your passport.