I am wondering if I can move my prefab garage across the building line so as to use the side of it as a wall (The old wooden fence was recently blown down in the wind).
If you mean bringing it forward in front of a straight line formed by the fronts of the houses then there's no point asking here - you'd better ask the Planners at your local council. Its something that requires PP. Or you could do it and move it back if the Planners object. They are only likely to know if one of your neighbours tells them. Perhaps check with them.