I have found a glitch with an incompatibility between Yoast and Betheme.
Firstly, Betheme, despite changing the site's tagline, does not erase "Just another Wordpress site" from pages when they are generated. If I leave the Betheme Meta description blank, by default "Just another..." is written into the page or posts meta description when it is published.
If I use the Yoast plugin, then that does not overwrite the "Just Another..." but creates a duplicate.
E.G.TitleFog | Ivor Rackham PhotographyMeta Description#1Just another WordPress site#2Fog brings some fantastic opportunities for photography. Enjoy this gallery of photos shot on misty, moist mornings in Northumberland.
I have searched the site's database for "Just another..." but it doesn't seem to be there. Is it somewhere in the site's WordPress file structure where I can delete it manually.
I have also asked a similar question on the Yoast support site. https://wordpress.org/support/topic/yoast-not-overwriting-just-another-wordpress-site/#new-topic-0