An old Victorian gas light on the corner of Church Row.
 
Victorian gas lighting emerged in London around the early 19th century, with early installations like those in Pall Mall in 1812, though widespread use came later. In Hampstead’s Church Row, these lamps evoke the era’s street illumination, predating electric lights that largely replaced them by the late 1800s. About 1,500 such lamps remain functional across London today, many protected by English Heritage. The above is unusually decorative but has unfortunately lost its gas system.
 
Interesting facts...
Always look up in interesting places, old fixings, signs and lights often are left in place providing traces of history. My other post for Hampstead even has an old French pocket watch above its window!