you need to fix those with a 301 redirect. if those are truly disk directories on an apache server, the mod_dir module should fix this for you. if these are "virtual directory" url paths generated by your CMS then your CMS should handle the redirect.
the other piece of that fix should include internally linking to only canonical urls (ii.e. trailing slashes for directory paths)
You may already have one too many Rewrites (not redirects).
The "real" location may be /vista-320-litre-box-roof-carrier-fits-audi-r8/index.html
or it may be /vista-320-litre-box-roof-carrier-fits-audi-r8.html
or it may be /complicatedstuff.php?long-ugly-query-here
But you can be absolutely sure that no more than one of your two names is the "real" location. So if they are both getting indexed, you or your CMS may be rewriting something that shouldn't be rewritten. Search engines know when they've been redirected but they don't know when they've been rewritten.