Some years ago, I was traveling with boat on the Thames east, I believe from Embankment to Greenwich. I believe this was on a regular TfL-boat, but I may have either accidentally gotten on the wrong boat (unlikely, or remember incorrectly)
On the upper deck, I found a man giving a "guided tour" of London as seen from the river. He spoke plenty about the buildings we could see, and told us varied information, from things like which celebrity lived where to what architects had drawn which house.
I'd like to re-take the same tour, but as far as I'm aware, this isn't normally organized by TfL, so I'm not sure where to look.
I missed the beginning of his talk, since he was already on at Embankment, but from what I did gather, he belonged to some sort of history society, and him giving the talk he did was a part of some kind of graduation ceremony. He collected donations at the end when we disembarked.
Any idea of what I was hearing, and/or where/when I can do it again?
The closest thing I've been able to find myself, it the sightseeing tours from London Eye but since those are paid, I assume they don't collect donations towards the end; nor do they end in Greenwich, making me think that's not what I was on.