Sorry I should have been slightly clearer, this code above is in the root directory of our main website, we also have a second htaccess file in root directory of WordPress which is the basic WP coding as below. However, it is the above code that stops me from accessing work-admin dashboard and if I rename (ie disable) the htaccess file above to see if I can get in to dashboard I can get in but I then get a message to say not authorised to get into our home page of our main website which is obviously no good.
# BEGIN WordPress
RewriteEngine On
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
# END WordPress