The Origin of Keep Calm and Carry On

When I was at Barnes and Noble yesterday, I saw notebooks, coffee cups and other various items stamped with, "Keep Calm and Carry On."  It got me thinking about it's origin.  There is no denying it's impact in the last few years on the crafting community.  It's been customized over and over again.

Keep Calm and Eat a Cupcake
Keep Calm and Rock On
Keep Calm and Call Batman
Keep Calm and Love On

You get the point.  Anyways, I wasn't sure I would find the origin of where it came from, but while surfing the internet last night, I came across a video that explains just that.  Enjoy!