mIRC provides a place for you to do this in the servers dialog.

options (alt+o) > connect > servers

Find the network (ukchatterbox) in the list and expand it, select the server and click the edit button, then add your password there. You can do the same for each server listed under ukchatterbox if there are more than one. If the network isn't in your servers list, you can add it in this same area.

Although I think you'll find what you need above, if you still want a script to do it, I think it would probably be the LOGON event instead of CONNECT...

Code:

on *:LOGON: {
  if ($network == ukchatterbox) {
    nick Silent_One
    pass *password*
  }
}