Do not despair. We still have a blimp.
A laughable 20-foot balloon.
It was supposed to trigger Trump's ego into some sort of meltdown, but failed, in 2018 and again in 2019.
But thanks for posting a picture from Parliament Square that illustrates how visible it was not outside of that tiny park in London. That area was ~2/3 surrounded by trees, as seen in your picture or on Google Maps Satellite View. On the other sides, Westminster Abbey, the Palace of Westminster, and Westminster Station blocked seeing it to the south, from the Thames, or the other side of the Thames. Street access to that park is also fairly limited, limiting the number of people who could get there and making it very easy for police to respond from a station a block or two away.