It means that HTTP and HTTPS works for www.mydomain.co.uk reolving to 188.8.131.52 The virtual hsot has to be IP based to support SSL.
* how do I stop requests to h tt p://184.108.40.206 returning the website? More specificaly, how do I make the virtual host *only* respond to requests for www.mydomain.co.uk?
I also have a new domain, www.my2nddomain.co.uk. I've setup an A record resolving www.my2nddomain.co.uk to 220.127.116.11 (same IP as above). Requests for www.my2nddomain.co.uk return my www.mydomain.co.uk website. Again, another situation where the virtual host needs to respond only to requests for www.mydomain.co.uk.
The first virtual host you define is the default virtual host and response to every request. So you could make a dummy virtual host as the first one with a blank page and the second virtual host with the domain you want.
how do I stop requests to 18.104.22.168 returning the website?
What do you want them to do instead? Blank page, alternate page, redirect to named site? There are probably a couple of other options. The address exists, so you can't say "ain't no such place", though you might find the Internet equivalent of "go around the back" or "please use the service entrance".