FL, This ties in precisely with my earlier post about the idea of a minimum altitude being introduced for that section along the river. I was shot down in flames by a number of posters who didn't want to see any more regulations.
I think you were the one who advised "be careful what you wish for"
A higher altitude would be of some use but obviously not if the cloud were low on the day. Also, as we know, twin engined helicopters don't have to stay on the river.