alexleonard – thanks so much for your quick response.
I think the first time I tried to create the htaccess file (since there wasn’t one in the WP directory) I may not have created the file properly (not txt) and so caused all these subsequent problems.
I’ve just tried again (a little more carefully this time) and fixed it! By creating a blank txt file called htaccess.txt, uploading it to the WP directory, renaming it to .htaccess and changing the permissions so that the dashboard can write to it. Then went back to the permalink options page and set them again. Did not get the Change Your Htaccess message from the dash this time round so I’m pretty certain it was able to do what it needed to do. Also – can access my other pages again!
Thanks again for your reply!