Icing can occur at Plus 10°C OAT
That may be so for your aircraft Sir, the aircraft I flew used +5°C as the switch on point.
For any aircraft type which is certificated for flight in icing conditions, the AFM or POH will contain a manufacturer’s definition of the threshold for ‘Icing Conditions’ for the purposes of the selection or activation of
ice protection equipment. This is usually given as the presence of visible moisture and an Outside Air Temperature (OAT), Static Air Temperature (SAT) or Total Air Temperature (TAT) reading of less than a figure between +3°C and +10°C. Operation of anti icing systems is never based upon the appearance of visible ice or on the flight deck annunciation of external ice detector activation, although de icing systems may be. Visible moisture can be defined in flight as clouds, fog with visibility of 1500m or less, and precipitation. On the ground this can include standing water, slush or snow present on the taxiways or runways.
https://www.skybrary.aero/index.php/...ht_Icing_Risks