Hi Shaun,
Thanks for the reply.
The closest I've got so far is modifying the line at the top of login.tpl that checks if is an incorrect login to this -
{if $incorrect} <meta http-equiv="refresh" content="0; url=https://mysite.com/custlogin.html"> {/if}
This works but it briefly loads the normal customer area before redirecting to my site.
It looks like I can't use a PHP header line as text has already been sent to the browser, and I don't want to have to rely on javascript being enabled on the client.
I guess I could check out doing a redirect using .htaccess if there's nothing in WHCMS to help with it?
Thanks, Matt