Via the Guardian (over a year ago, but I'd never seen it), which has more information:
In 1926, London Underground published a poster painted by Montague B Black, a publicity artist who also created images for Liverpool’s White Star Line, which imagines London in 2026. A golden sky enfolds a cityscape of skyscrapers over which various types of flying machine hover.
We've still got 10 years to go...
|Click here to embiggen|
Related, also at the Guardian: the London skyline 1616 v 2016