postcard.co.uk

What are these things by the edge of the road which look like parking meters? They are red, postalheritage.org.uk says
"In 1897, to answer the demand for more convenient posting facilities for London squares (around which were the houses of some of London’s more influential residents), small boxes were designed. The boxes, made to attach to existing lamp posts, and big enough only to hold small letters, soon began appearing in low volume areas around the country (and disappeared from the London squares)." but these look impractically small for a public road.

http://rthcards.co.uk/images/Kew%20Gard ... 207562.jpg

http://rthcards.co.uk/images/Castlenau% ... k%20id.jpg

A good observation - I don't believe these are postboxes... but which did exist, however, attached to poles with 'D' clamps and were designed to accommodate letters only.

A debate as to what they are can be found, with a great Postcard example, here: http://www.harringayonline.com/photo/ed ... ightman-rd

Thanks! Quoting from the last response by Lesley Ramm "These are street fire alarms and became common in the second half of the 19thC after the Telegraph system was installed." I'll buy this as the answer, though the examples in close up all have a rather different shape at the top.
Interesting that the exchange you found was mainly in 2013 but the final input was only a few weeks ago!
Incidentally I find that there are lots of them for sale on ebay, though presumably all US ones.

Nice! Do I sense a new collecting theme here?

One might need a bigger house! Another topic I have looked up, with only partial success, is identifying and dating old street lights in postcards, and I came across web sites of people who have quite extensive collections of lights, including complete lamp standards. When I started collecting postcards I thought they were ideal because they didn't cost much and they didn't take up much room, but even this isn't quite the case.