Ok, so the file is working, thats a good start!
Looks like we need to go back a step in the request process then. Do you have access to the DNS settings for the http://atp-instrumentation.co.uk domain? If so, please could you check if there is an A record set for it? (looks to be registered through Civica UK Ltd - Whois Report)
What i suspect might be the case is that you're missing an A record for atp-instrumentation.co.uk but that there is one set for the www.atp-instrumentation.co.uk.
I've run a couple of tests against the domain DNS and i get nothing back for the non-www address, which is what suggests that we're not even making it as far as your servers.
To set the A record, you'll be looking for something in your control panel for 'DNS settings' or maybe 'Host Records', you should see in there ether an option to select A record settings, or perhaps a dropdown with things like A, AAA, CNAME etc. You need to:
Hopefully that makes sense. If your at all unsure, let me know and i'll do what i can to help more specifically. Domain control panels are so different for each provider its difficult to provide direct instructions without knowing what your panel looks like