http://www.safari.co.uk/kenya/index.html - Works, not so perfect! As this page doesnt exist and should be coming up with a 404 really instead of the kenya page? This is allowing google to see the page a duplicate content.
It's not SilverStripes fault, it assumes index.html is an action of /kenya so has no reason to do anything about it.
Unless you're linking to index.html, Google should never even bother to look for it so it wouldn't be a problem.
There are a few options if you want to get rid of it. You could get block *.html in robots.txt, use a rewrite in .htaccess to redirect any instances of *.html, add custom code to the controller to return a 404 if the last URL segment contains .html or use the canonical meta tag to avoid any duplicate content issues.