I pulled this out in two halves about 45 minutes apart from each other. The second half had numbers on it that I thought could be a date, but on further inspection of the first half it looks like the numbers continue on it, so unfortunately I don’t think this was cast in 1828.
I got far more than I was expecting at this spot, given that it’s on the edge of a village rather than city centre, including a still working fire extinguisher:
A car stereo amongst some other bits:
And the most nails I’ve ever found in a single trip by far, with the stuff I didn’t find particularly interesting:
My guess, something like that
That sounds very plausible, I can imagine the four tabs around the opening clamping down on the bollard, with a slot at each corner to bolt it down. Also it’s something that would probably be thrown in the canal after being illegitimately removed.