Start a day ahead. Mix the olive oil, ginger, garlic, sherry and soy sauce together. Place the fillet in a shallow dish. Pour the marinade over the meat. Cover and place in the fridge overnight, turn occasionally.
Set oven at Gas Mark 6, 200ºC (400ºF).
Lift the meat onto a roasting tin. Reserve the marinade. Roast the fillet, allowing 8 minutes per pound for rare and 10 minutes per pound for medium, or use a meat thermometer. Brush the fillet during cooking with the marinade.
When the meat is cooked wrap in foil to keep warm. Deglaze the pan with the wine. Stir over a high heat gathering up the juices. Add a little water if necessary. Add in the scallions and season to taste. Slice the fillet and serve with the sauce.