Can't speak for the UK, but I often see Smarts parked sideways around Paris. The car is indeed longer than the spaces are large, but a factor that helps a lot is that regular cars are rarely parked nicely inside the lines. Which means that, in practice, the sideways Smart doesn't stick out from the other cars.

> The car is indeed longer than the spaces are large

Assuming your native language is French, I think you mean “wide”, not “large”.

I see them parked sideways in London all the time.

Same in Prague.

never seen in Italy

They have elongated. The first ones were shorter. The park sideways gimmick was part of the original marketing, now they are longer that aspect is not advertised as a feature.

Sideways parking would be a killer feature if it actually worked, but they're just a bit too long for that, and according to my memory, have always been.