Single Carriageway with 3 Lanes?

What is a Single Carriageway with 3 Lanes as described in Highway code Rule 135.

Where a single carriageway has three lanes and the road markings or signs do not give priority to traffic in either direction use the middle lane only for overtaking or turning right. Remember, you have no more right to use the middle lane than a driver coming from the opposite direction do not use the right-hand lane.

Can anyone plz share a picture of such a lane? Is the middle lane used here for dividing the opposite traffic?

They used to be called widow's highways because they are really dangerous, there used to be a section of the North Circular in London that had this arrangement but I don't know if it is still there. Essentially any traffic can use the middle lane in both directions to overtake. It is not used to separate traffic. So you move into the middle lane in either direction to overtake and then move back. Whether you survive or not it dependent on the reflexes of the drivers coming in the opposite direction. No one would ever take a learner out on one for their test. I don't have a picture but its just three lanes with normal markings.