I had an incident in Braunston Tunnel a couple of years ago. There was a boat following us quite close behind, which was very annoying, blinding us with his tunnel light. We couldn't go any faster, as there was a third boat a liitle way in front of us. Another boat came the other way, travelling too quickly. As he passed us, both of our boats swung into the centre of the tunnel due to the suction effect. He went smack into the boat that was too close behind us. We were fine, not a touch, but there were lot of raised voices behind us as we left.
So: Slow down when you meet another boat, and don't go too close behind the one in front.
James