The colleges are large, set back from the street and in their own grounds. While paths around the colleges are I'm sure lit, there is no light onto the buildings themselves and standing at the back of Kings College to try to capture the above picture at night, the college was hardly visible to the naked eye. That said, I was not going to let this stop me.
The result I achieved is shown below and I'm pretty happy with it. In many ways, it looks absolutely fine and you could be forgiven for thinking that I'm making up about how dark it was, but I'm not. The exposure time for this picture was 5 minutes at ISO 200 at f/8. That is pretty much the longest exposure I've ever done with the camera. Compare with my Oxford pictures where for the Radcliffe Camera at f/8 I was 100 seconds at ISO 100. In other words, I'm double the ISO and triple the exposure. There was a lot of standing around that night.
You can see stars streaking across the sky leaving light trails so the hot pixels are easily separated from stars. The problem is, there are far too many of them for spot healing or the like, and ordinary noise reduction in Lightroom didn't really seem to fix the problem (but possibly I didn't get the sliders right to do so), so what to do?
Just to note, the filters/noise/despeckle filter, an obvious choice for this problem, significantly reduces the impact of the hot pixels but on this image at least, reduces their impact rather than eliminates them.
On this occasion though, the DxO Optics software really did do the job well. A 5 minute exposure at ISO 200 is pretty extreme and this is the first time that I am aware of that I have been materially impacted by hot pixels. But now it seems I also know how to fix them.