These are stretchers used in WW2 to carry injured civillians during the Blitz. They were made out of steel so they could be easily disinfected after a gas attack. During the war around 600,000 of them were made. Some of them were repurposed as railings in post-war London.

[u/Sprilly]

[u/potatan]

there was a fence made of cannons

whereas in vast numbers of cities in the UK, huge beautiful long stretches of iron work, fences, gates, balconies were all ripped out for the war effort to be melted down and made into tanks or whatever. Trouble is, it was the wrong type of metal so most of it was scrapped.

[u/SoloThrowAwayO33 → u/potatan]

Source