Well just had to install Highslide js. It is lovely to use and better than any slideshow.
There isn’t a plug-in for gallery2. But the technique is to install Lightbox js – which takes a bit of doing. Then uninstall it and install Highslide using the same technique.
It became obvious that although Gallery2 works out of the box – playing about with this leviathan is long-winded in the extreme. No it has to go.