You should contact the Pensionsversicherungsanstalt & ask for “Überprüfung der Anspruchsvoraussetzungen” & “Versicherungszeiten”, they should send you a form to fill in where you can state your NI periods in UK – PVA will then contact UK authority & do the work for you.
You don’t have to do this – PVA will do it automatically when you claim your Austrian pension, but if they already have your NICs data the process will be more speedy.
Probably a good idea to do it as UK authority currently very sluggish.