I seem to remember Barnes Wallis saying that he had a basic design for an aircraft, which could fly from the UK to
Australia in four hours.

So do I.
Heck, anyone with a pencil and a piece of paper can do that.
The hard part is the detail design…not to mention the money (and political will) to build it.

A SST isn’t coming along soon.
I don’t see the UK or the EU building anything of the sort. It’s perceived as too “ungreen”.
Especially in the UK where government policy seems to be “tax people into being green”. What’s the tax rate on petrol..60%?
So what you have is a return to the 19th century class system…the upper classes (now days that means celebrities instead of the titled) can do what they want because they can afford it…while the regular people are herded onto busses.