When we were going through Harecastle tunnel earlier this year, the chap on the boat in front of us proudly produced a bugle when asked to demonstrate/test his horn.    The CRT chap refused to accept it as a working horn - he made the boater blow all the air out of his lungs then try and use the bugle, which obviously didn't work.  He then gave the boater a compressed air cylinder horn which they gave back at the other end of the tunnel.