I think I have a method that works [for removal of Sophos] It might seem a bit convoluted but as I say I think it does the job.
1. Uninstall Sophos components [Sophos Anti-Virus, Sophos Auto Update and Sophos Remote Management System]
2. Restart as required.
3. Perform file and folder search for Sophos remnants [SophosNoUpgrade.txt, Sophos AutoUpdate install log.txt etc] and delete files found.
4. Use Registry Distiller to remove any Registry fragments left behind by the uninstall routine]
[Please test on a machine that you are happy to re-image/re-build before testing on your 'target' machine]
Registry Distiller Link: Registry Distiller - Download
[Can be downloaded using other URLs]
Hope this helps.