Following the 'Browse for the bloat' advice and exploring the various folders I came across some similar files which rang no bells at all. They were Untitled-061112-234451-001... , ...3, ...4 and some were around 3.99GB each. Underneath then were the letters NBF. Finaly managed to identify them as BackupNow archives made some time ago and that particular program had been deleted in the search for space. Upon deleting just one to gingerly experiment, hey presto
space appeared on the hard drive.
Thanks all for the advice and help, it was much appreciated.