Many thanks to those who offered advice on this.
The issue is now CLOSED, not because I've fixed the problem, but because I decided to uprade from httpd 2.0.19 to 2.2.4.
I have been putting this off for some time, due to possible difficulties with mod_auth_mysql, on which many of my applications are dependent.
SSL worked straight off, when I did this; it did mean that I have spent most of the day fixing all the other issues - like getting mod_auth_mysql working (there's a patch available) - rebuilding PHP (twice), etc, etc.
Now all working fine on my backup Linode; will install on my production Linode early one morning, before my clients are awake
