HuskyPup - 3:30 pm on Mar 12, 2011 (gmt 0)
I have redirected them all to point to mymainsite.com in my control panel.
Are you referring to your registrar's control panel or cpanel?
I needed to register a domain with new extension and use it as an aliases on mymainsite.com.
Why an alias? Are you trying to mask the original domain and serve precisely the same site yet showing your new domain names with a new title bar and meta description?
If so this is old, old stuff and won't get you anywhere in the search engines since they won't rank highly because they are duplicates, they won't be penalised, just very unlikely to rank.
If you want you example.co.uk to point at example.com you should be able to create a url-forward in your registrar's control panel.
Do ensure that it is a 301 and not a 302!