I have an existing website www.domain.ie. I want to get more traffic from the Uk so I bought another site, www.domainltd.co.uk. I want to setup the second domain as an alias for the first, i.e. I type in www.domainltd.co.uk, but I am re-directed to www.domain.ie. I thought that setting up the alias in the Control Panel from the hosting provider of domin.ie would magically sort this, but no.

I' m looking for the steps I need to take so that if i type www.domainltd.co.uk I get re-directed to www.domain.ie.
I assume that this is called setting up an alias?

Any help appreciated.

Did you try the hosting providers alias setup? It would also take some time to propogate the DNS settings, so give it some time (ie 8-12 hours). It should work.