Drush can not find settings.php
I was right in my comment earlier. The issue was compatibility between drush 9 and drupal 7. Once I downgraded to drush 8.1.10 it worked fine. Note there is also an oddity with 1and1 specifically where in SSH they default to php4.4 which is too old! So I also had to set up an alias for php and php-cli to refer to a more modern php. Also I had to ensure drush used it by adding 'export DRUSH_PHP=' followed by the full path and filename for the more recent version of php.

If anyone reading this does not know how to downgrade drush with composer you have to remove and re add it with the following commands:

composer global remove drush/drush

composer global require drush/drush:8.1.10

Replace the 8.1.10 with the version that you want.

Also, anyone new to composer might get fooled as I did by the prompt 'Discard changes? (y/n/v/d/s/?). Yes actually means 'discard and apply changes'! I found details of this in the following post:
https://stackoverflow.com/questions/25828102/composer-discard-changes-what-do-the-y-n-v-d-s-do

I hope this helps anyone else new like me stumbling across this issue!

Once again thanks for the comments - the one question from @Christia about drupal version triggered me to look in the right direction!

Rory