Apart from the fact that the jQuery is called twice (once hard coded in header.php and once by WordPress) and the roundiesDD.js script is called three times, I see no errors that could cause this.
Did you try activating the iFrame feature in the Media > FancyBox settings and use class="fancybox-iframe" already?
Yeah it’s working elsewhere, try ‘Terms and Conditions’ in the footer, that works on every page of the site.
P.S. I’ve tidied up the other javascript now.
There is still the issue of double loading jQuery library, plus there is the <html> tag missing but that’s not the cause.
It seems like the script(s) in http://www.mercersofyorkshire.co.uk/wp-content/plugins/woocommerce/assets/js/woocommerce_plugins.min.js do something to the checkout form content, breaking the fancybox attachment. It seems to reload the bottom part. Everything after the selection option of the payment method gets refreshed.
Is there any way to place the terms+conditions link higher up on the form? Above the payment selection field?
