Do you want to check these and see if this is the issue or is it to custom to make changes ....... https://jigsaw.w3.org/css-validator/validator?uri=x-on.co.uk%2Fcontact.html&profile=css3svg&usermedium=all&warning=1&vextwarning=&lang=en

Your HTML is perfect.

Please let us know if this solved your issue or if need further assistance

Thanks for running the report - interesting, a lot of CSS issues there - we'll review.

Stripping all CSS from the contact.html down to a bare bones form doesn't help.

We've realised however that the form, even with all the CSS applied, does submit if we submit from a local test of the overlaid contact form, but not from the live site overlaid contact form, which is odd.

Presumably it's feasible that it's something to do with the hosting - we're about to change the hosting so it will be interesting to see if that helps.

Thanks again for your help.

I tested in a private window. On the first try, Firefox logged this in the Browser Console:

The resource at “https://webto.salesforce.com/servlet/servlet.WebToLead?encoding=UTF-8” was blocked because tracking protection is enabled.

After turning off tracking protection, which reloads the page, and filling some sample data, the form submitted the second time.

Since I use NoScript, I then allowed Salesforce.com and submitted again.

I then allowed Google Analytics and submitted again.

Look for up to three contacts from joebloggs@example.com.

Fantastic! That's it.

We'll add a note re tracking to the form for visitors unable to submit.

Thank you for taking the time to investigate/test/respond.

MUCH APPRECIATED!!