After descending below cloud to the south-east of the Isle of Wight, using Portsmouth VDF, a visual approach was made followed by an unsuccessful attempt to land on the 07 grass strip. A further circuit was made and the aircraft landed on the same strip. Ground fine propeller pitch was selected immediately after touchdown and the brakes were applied shortly afterwards. The grass was wet and, after some initial deceleration, further braking was ineffective and the aircraft ran through the fence alongside the main road in the northeast corner of the aerodrome and came to rest across the road. The aircraft was extensively damaged but there was no fire and there were no injuries to passengers or crew. CAUSE: “The primary cause was the inadequate braking which resulted from the extremely low coefficient of friction provided by the very wet grass over the hard, dry and almost impermeable sub-soil of the aerodrome. The fact that no account had been taken of the extra landing distance necessary for HS 748 aircraft on wet grass must be considered as a contributory cause since had this been applied Channel Airways HS 748 operation at Portsmouth would not have taken place.