http://www.avclub.com/article/late-majel-barrett-might-still...
http://www.npr.org/sections/money/2015/12/09/459116467/episo...
There's a transcript here:
http://www.npr.org/templates/transcript/transcript.php?story...
One of the ads: https://www.youtube.com/watch?v=kpPzcAseU8E
EDIT: See the NPR Planet Money podcast linked elsewhere in the comments. Apparently there are fairly specific laws to protect someone's likeness -- including their voice -- thanks to the entertainment industry and Frank Sinatra.
I guess he had a strong case because in all three cases he was (or so he claimed) approached to do a commercial and the advertisers went with a Waits-like surrogate after he declined.
Trademark/Copyright can't be disclaimed in this way but Passing Off requires active deception AIUI?
You're right that being clear to avoid confusion is a good preventative measure, but you're wrong that intent to defraud is required. It's enough that the public is (or is likely to be) confused.
See Reckitt v Borden (1990) judgement referring to the three-part test for claims of passing off (my emphasis):
"Second, he must demonstrate a misrepresentation by the defendant to the public (whether or not intentional) leading or likely to lead the public to believe that goods or services offered by him are the goods or services of the plaintiff"
It might be worth noting Mickey Mouse is a registered trademark and so doesn't need to use the weaker Passing Off law?