Hello,
I got it all wrong at the first look.
Here is what I would suggest: As Thomas said, you will have to add an A record to point www-mydomain.co.uk to point the IP address of our server in your local DNS.
You will not be able to access your web site hosting with the IP (that is
http://91.186.30.8) but after you point your domain to that IP you will be able to access it with
http://www-mydomain.co.uk since there are two completely different methods involved to display the pages through that URLs.