Don't know if it will help, but try leaving the hyperlinks panel open, and if you can live without them, turn off page thumbnails in the Pages panel. Turn off live preflight, too.
Hi Peter, Thank you. It did prompt me to do something now normal service has resumed.
Live pre-flight has always been fine but there again I have applied my own optimised settings. The thumbnails are always off in the pages panel – no need to have them on really. However, 'closing' the Hyperlinks panel has meant normal speeds have returned. It seems my working practice would need to change by checking all the hyperlinks at the end instead of having the ability of working through them on-the-fly. I have also unchecked the 'Auto Update URL Status' in the Hyperlink panel's settings but not sure if this is making the difference.
I don't work with hyperlinks in my workflow, but I'm fairly sure the auto-update is the culprit here.