Thanks for trying to help.
I want the site run on my local development machine at 127.0.0.1 (dnndev.me). The problem is that having copied the site from live to development, ensuring the dnndev.me alias is present, when I navigate to http://dnndev.me in my local development machine browser, it immediately redirects to http://<livesite>/en-gb/ , which is in any case invalid (404) as there is only one language enabled, en-gb. There is a setting "Enable Language Parameter in URLs?" under language management, but when I uncheck this, nothing changes and the next time I return to the form - the box is checked again anyway. Under normal circumstances the site just runs at http://<livesite> (i.e. no /en-gb/ in the URL.
You say each language has to have a primary alias - how is that determined/set? I have just two aliases, <livesite> and dnndev.me. I can't edit the <livesite> alias because under normal circumstance that is the alias in use. And I can't change it on my development machine, because it immediately redirects to the live site. I seem to be in a catch-22.
I am sure I am missing something, but I haven't had this problem before when developing modules, although this is the first under 7.3.
At the moment I am trying re-installing a blank version of 7.3 just to allow me to continue working on the module - not ideal as I really want to test it in the context of the real site and need to be able to pull back a copy of the live site for full testing.