by Pascal Zajac.
Consider this withdrawn, the problem wound up lying with my MySQLserver which was unable to write to the /tmp folder on my server. Once I rectified this, the upgrade proceeded without issue.
Incidentally, the above post proved to be a red herring - the problem was actually that the get_columns call was returning an empty array (if the MySQL query to obtain table information fails, an empty array is returned, which can be quite confusing when success was expected). This masked the true failings of my MySQL server.
Everything is back up and running.