Hi,
Last night I disabled the Siteground plugin as you suggested. I think your developers checked after i had done that which is why they saw it working.
You were right, it was the minify javascript within that plugin that was causing the problem. I have now enabled the plugin in again but disabled the minify javascript and updated the Theme on the live site and as far as I can see the checkout is working fine.
i wonder if you could just please check again the live site checkout in case I am looking at anything that may be cached. If you see it working then all is fine. I have notified Siteground as I need this plugin, it’s part of my hosting and hopefully they can work in a fix on their next update.
Thank you for all your help with this. Debbie