It's OK, I figured it out in the end. This is what I do, after opening a window of whatever size is necessary (1920x1080, 800x600, etc etc). My graphics were produced for a default resolution of 1024x768.
int scrW = graphicsBaseSizeW; //1024 for this game
int scrH = graphicsBaseSizeH; //768 for this game
window1View = window1.GetView();
window1View.Reset(sf::FloatRect(0,0,scrW,scrH));
window1View.SetViewport(sf::FloatRect(0,0,1,1));
window1View.SetSize(scrW,scrH);
window1View.SetCenter((scrW/2),(scrH/2));
window1.SetView(window1View);
Hope this helps someone in future...
Ed