Thanks very much. This was very helpful and has pointed me in the right direction. I have now set up admin and mailback templates and all is working perfectly except for one thing.
When I navigate to the 'Contact us' page on the website, the page height starts to increase from around 3000 and doesn't stop. If I switch to another tab and then back, it starts again. This happens on both Chrome and my mobile browser.
I am not sure if it is a bug and probably not a big issue but I thought I should let you know.
See screenshot from my Chrome browser attached for the code.
That has certainly fixed it but the submit button was then hidden under the footer on my mobile after I added the Mailback option. Changing it from 500 to 600 fixed it so thanks again.
Something to watch for when building my forms in future.