Michael Gove asks in his column:

Just what does it mean when we say that butter
wouldn’t melt in someone’s mouth? And where does the phrase come from?
Answers, please, to michael@michaelgove.com . . .

Go to http://www.google.com. Enter the phrase. Hit "I Feel Lucky".

Worldwidewords. Michael Quinion, a researcher for the OED.

It’s one of those sayings that are so old their origins are lost in
the proverbial mists of time. It refers dismissively to somebody who
appears gentle or innocent while typically being the opposite. A
typical use was in William Makepeace Thackeray’s Pendennis:
“When a visitor comes in, she smiles and languishes, you’d think that
butter wouldn’t melt in her mouth: and the minute he is gone, very
likely, she flares up like a little demon, and says things fit to send
you wild”.

It appeared in print first in John Palsgrove’s book about the French language, Lesclarcissement de la Langue Françoyse of 1530, but it’s more than likely he was borrowing a saying that was already proverbial. (There’s more if you want it.)

Mr Gove MP? Meet Mr. Google. Mr. Google? Meet Mr Gove MP. Mr Gove MP? Mr. Google is your friend.

(This post has been supported by the Google Inc press relations department.)