Hi Peter,
I examined the file. It looks very much like it was processed as a pdf prior to re-conversion to SVG.
You can select the largest group, then ungroup a number of times to get the objects completely separated (watch the information area in the status bar at the bottom of the screen). You can also see an inventory of all objects in the Objects dialog (Menu: Object>Objects). Once you ungroup repeatedly until there are no more groups, you can proceed.
You will find a number of embedded images used as clipping objects; they can be deleted without issue.
Chime back and keep us posted.
Have a nice day.
TD