Many years ago, I travelled from Winchester to London on a semi-fast service worked by a SWT 4-CEP unit. On the non-stop run from Basingstoke to Woking, the driver sounded the horn on the approach to each of the intermediate stations (Hook, Winchfield, etc). I never understood why, as we were on the up fast line which does not run adjacent to any platforms on this stretch. It seems unlikely there were p-way staff on the line at each of the five stations, and I certainly didn't see any from the train (although they could have been on the opposite side).