On 2017\08\08 11:54, Recliner wrote:

That's true of most Tube tunnel portals, as the initial shallow
section is cut and cover. The TBMs only do the deep tunneling.

I've just looked at numerous tube portals in Bing Maps using the 45
degree view. The pair of round portals are clearly visible in most. I
have found none which clearly match your description.