You set this up in CPanel on your iweb space as add on domains (this parameter never seems to be set up properly so you may need to raise a ticket), then you add them on there and it automatically points them to the same space in the same way the
www.xxx.co.uk and the xxx.co.uk and if you've set them up https:// all point to the same html folder.
Having used UK2 for hosting in the past, personally I'd bite the bullet and move the whole hosting, images an all to one place, iWeb, that way your html can have relational links (e.g /images/file1.gif) rather than full
http://www.theothersiteonuk2.co.uk/images/file1.gif).
Your tracking stats etc on the iWeb interface will show all traffic too.
I've sent you a PM so you can see how it works when set up on cPanel in iWeb. I don't want to publish the domain names here as it confuses search rankings having a wedding site on a cable forum.