Bristol has them and I thought I'd seen them in various other places, but I've just read that they're pretty much restricted to here:
https://www.bristolpost.co.uk/news/bristol-news/you-see-iron-pavement-edges-2941271Leeds and Southampton were quick to follow suit, and examples of this iron edging can be found in those cities too, but nowhere has as much as Bristol.
I suspected local acts of journalism but a quick search turned up several photos of such kerbs labelled as being distinctively Bristolian and this, which added a little more detail on their local origins:
https://www.about-bristol.co.uk/eye-05.aspA distinctive iron pavement kerbing was frequently used in Bristol streets, to prevent iron cartwheels damaging the stone paving. Many sections of the old edging still exist - Lower Park Row (below left) and Temple Street (below right) are typical examples. The iron kerb is almost unique to Bristol, Southampton being one of the few other places.
Iron kerbs were still being installed in the early 20th Century, when they were made by the Douglas Company of Kingswood. They used surplus metal left over from manufacture of their famous motorcycles.
Douglas motorbikes were known for their flat-twin engines, similar to those used by BMW, but I'm not sure if there's any connection between the two firms. But given the industrial connection, you might expect iron kerbs to be common in places like Coventry and Birmingham, though obviously there could be a distinctive Bristol design.
So who's got metal kerbs? Are they really geographically restricted?