Nginx is configured to use /var/www/vhosts/folders.cordelia-malthere.com/httpdocs and Certbot is configured to use /var/www/vhosts/folders.cordelia-malthere.co.uk/httpdocs. Notice one is “.com” and one is “.co.uk”.
Nginx’s error.log can probably confirm that that’s the issue.
You can run “certbot certonly” with the same options used to originally create the certificate, with that one path modified, or you can edit the /etc/letsencrypt/renewal/ config file in a text editor to adjust it (while being careful not to change anything else).