Scheduled Job not executing with wp-cli under cron, but works manually
To analyse this, as suggested by @Aidan I redirected the cron output to a file by adding this string to the end of the cron command:

&amp;&gt; /var/sites/d/mydomain/logs/cron.log


This showed that the command was failing with "Fatal error: Class 'Phar' not found in /var/sites/d/mydomain/wp on line 3"

Having queried this with my hosting support, it turned out that the implicit version of PHP called from cron was 5.4, but from SSH terminal, it defaulted to 7.0.  Once I explicity called v7.0 php at the front of the cron command as below, it ran fine:

/usr/bin/php-7.0 /var/sites/d/mydomain/wp etc