Function Key . 
F0   Side Lights  (Directional)
F1   Sound On/Off.
F2   Short Horn 1.
F3   Standard Horn 2.
F4   Buffer Clash/Coupling.      (Coupling up only when stationery)
F5   Active Braking.                 CV179 Adjusts Braking intensity
F6   Emergency Braking.          CV180 Adjusts Braking intensity  
F7   Drive Lock/Hold.
F8   Automatic Uncoupling.
F9   Flange Squeel.                 (If Moving)
F10 Despatch Whistle.
F11 Wagon Buffer Clash.         (If Moving)
F12 Radio Communications  = Class 071 Only
F13 Station Announcements.   CV155 0-8 Changes Station Names
F14 Roof Fans.
F15 Cab Lights.
F16 HEP (Head End Power)     (Class 201 Only)
F17 Light Load/Light Engine.
F18 Heavy Load                     (Will override F17 'If On').
F19 Head Light.
F20 Train Mode Lighting: (Red Tail Lights 'off' on Class 071 Only).
F21 Not Used.
F22 Wagon Rail Noise             (If Moving). 
F23 Loco Coasting.
F24 Not Used. 
F25 Rail Noise.
F26 Sanding. 
F27 Compressor.