Google Maps shows it better, this is the view when you have to decide whether to 'commit' to the tunnel or not. (The direction the old man was coming from):-
Visibility is not great because of the slight bend and due to the fact we drive on the left.
https://www.google.co.uk/maps/@51.5...4!1sKo2ySuO2oQMNlZgFby_Iqg!2e0!7i13312!8i6656
This is the direction the woman came from:-
https://www.google.co.uk/maps/@51.5...4!1s_ztpV758CtxZMvjvw2wV5g!2e0!7i13312!8i6656
I've been through that tunnel hundreds of times and it does happen every so often that someone decides that even thought your 3/4 of the way through, that you should be the one to reverse and they can't wait 5 seconds. The other issue is that at peak times, if you are the one with priority, cars will start flowing through from the other side and you can end up there for ages before someone takes notice of the give way sign.