Hi Mark,
From the log, it appears that the issue is that UpdraftPlus is not able to write to the disk due to a lack of space. For example, in this case, there only appears to be ~457MB available to UpdraftPlus.
While there may be more free disk space inn your account as a whole, it appears that there is a smaller limit on the quota assigned to the webserver account that PHP (and so UpdraftPlus) is running under.
I would recommend contacting your hosts and ask them to confirm the amount of free space available to the site.
Best Wishes,
David N