I have just tried the Webmaster Tools for Google and Bing using the place meta tag option in each. Verification failed. I read another forum post on this topic and as I use WP Supercavhe, I cleared the cache and tried again. Same result.
used Firebug to heave a look at the Head section of the site and there is no meta tag there relating to Google or Bing.
I do have the Use meta keywords tag on if that is relevant.
I haven't had a problem with any other of the Yoast SEO settings e.g. sitemap is working.
Any ideas will be welcome thank you.