Slow backups since 9.5 installed

Hi there

I've installed 9.5 over the Christmas period, and our backups are now running much more slowly, despite us still issuing a net stop savservice before running the backup.

The Sophos logs appear to show that the on-access scanning is re-starting itself during the backup window - I've read this could be to do with the automatic update.

How can I stop Sophos re-starting on-access scanning until it is clear to do so by the backup application?

Thanks

Alex