How common is it in current British usage for the angle between the chord line of a wing and the flight path to be called the "angle of incidence"?
From A.C. Kermode; Mechanics of Flight, London, Pitman, 8th Edn, 1972, p.75 (his bold):

&quot;We call the angle between the chord of the aerofoil and the direction of the airflow the angle of attack.
&quot;This angle is often known as the angle of incidence; the term was avoided in early editions of this book because it was apt to be confused with the riggers' angle of incidence, i.e. the angle between the chord of the aerofoil and some fixed datum line in the aeroplane. Now that aircraft are no longer &quot;rigged&quot; (in the old sense) there is no objection to the term angle of incidence; but by the same token there is no objection either to angle of attack, many pilots and others have become accustomed to it; it is almost universally used in America, and so we shall continue to use it in this edition.&quot;

And from L.J. Clancy; Aerodynamics, London, Pitman, 1975, p.56:

&quot;The attitude of the aerofoil, as expressed by the angle between the chord line and the free stream velocity vector ... , denoted by $\alpha$, is called the incidence, or angle of attack.&quot;

In contrast to Kermode, Clancy goes on to use &quot;incidence&quot; throughout. Note that this contrast appears in technical books from the same publisher, just three years apart. It was, and is, no big deal.
In my experience, anybody with the slightest technical interest in flight is familiar with both usages and they both still get used interchangeably in the UK.
I have not seen a standard symbol for the rigging angle, presumably because it is of irrelevance to the aerodynamicist. It was once, and occasionally still is, alternatively referred to by its French name of décalage.