This is the very classy "de Luxe" forged aluminium version of Holdworth's "Il Primo Milano" and comes from the 60s era. The badge is a lot more ornate than the earlier steel version and the stem is lighter and considerably higher quality too.
Holdsworth had these stems made by Cinelli, as I understand (since at that time they weren't used to working with alumnium), so it would be authentic and also look absolutely fine on either an English build or an Italian one.