Which assumes you've seen any other traffic. What about that small dark coloured car / motorcyclist entering from the slip road / hard-shoulder... the view of which was obscured by the lorry you've just overtaken ?
I was taught the same right enough, for lane changes you only need to signal if there is someone near you who might benefit from your signal... but I tend to signal anyway, just in case... maniacs pop-up out of nowhere these days.
Besides, signalling anyway is good practice, and gets you into the habit. How many people do we all see F*****G daily that don't signal before cutting you up, turning, stopping, exiting RAs, etc etc. :bang:
If I had a pound for every one of those.... :yum:
As a sidenote, the lane-change function on the newer Puntos, and probably I imagine pandas, 500s, 500Ls, etc... is a god-send. No more forgetting to cancel the signal.... although, for months after I got the car I thought it was broken