Here's a picture showing the "cut and cover" method used in the area for the early underground. http://guernseydonkey.com/?attachment_id=5522 Often the railway was built by digging out the roadway, which was then covered and the road re-instated. In some places however, where the railway was not covered, the supporting iron work could be seen as in your view.
Excuse double post. Here's a similar section of open underground track near Kings Cross. https://www.google.co.uk/maps/@51.530133,-0.1192307,210m/data=!3m1!1e3 There used to be many sections like this on the Circle Line. Over the years they have been built over, no doubt due to improved building methods and rising property values.
It's the Circle and District line running between Notting Hill Gate and Kensington High Street. Much of the Circle/District/Metropolitan lines are open to the sky n cuttings such as this. Just north of that location, on the stretch between Bayswater and Paddington, the line is similarly exposed as it crosses Leinster Gardens. Two dummy fascias built to resemble the adjacent terraced houses, conceal the exposed line from the street: