Я получил там в конце концов:
> SetEnvIf Referer
> ^https?:\/\/[^.]+\.(?>mydomain\.co\.uk|mydomain\.com).*$ refererok
>
> <Location />
> order deny,allow
> deny from all </Location>
>
> <Location /set2/>
> order deny,allow
> allow from all </Location>
>
> <Location /set1/>
> order deny,allow
> deny from all
> allow from env=refererok </Location>