I have a MacBook Pro that backs up to a Time Machine with no problems. However, the 250Gb hard drive of the Mac contains a 70Gb back up which eats significantly into the hard drive space. Is this necessary over and above the Time Machine backup and, if not, are there safe ways to reduce it?
I think what you're seeing are local snapshots that Time Machine uses. That would account for the 'backups' shown on the Storage tab. Usually these backups are deleted in a weeks time - they're just a temporary repository that can be used to recover data.
See Pondoni's article about local snapshots here -->> http://pondini.org/TM/30.html.