Your virus scanner should scan the restore folders.
SR makes a restore of the critical files so, if your virus scanner detects nothing then the SR files should not be infected as all it has done is copied the critical files (make sense?)
But the AV should scan the SR files and folders.
It has been assummed that if the SR files and folder are infected with a virus, you have to delete all SR points to delete th virus. But actually you do not have to delete all SR files - just the infected ones which the AV scanner should how (the infected folder, file)
"When I run my weekly virus check should I then, therefore, shut down system restore to enable a full scan in case of any latent viruses etc ?" - No your virus scanner should scan the SR.