My bike washed out on me twice today on a new bit of muddy singletrack, I know mud tends to be very slippy but I think it does vary because I wan't expecting it to give way like it did.
So where on this island is the most slippery mud?

The chalk……

It was in Rossendale a few weeks back, frozen base layer with a slick layer of semi melted mud on top, lethal.

It gets like butter in places on the Mendip.

As CFH says. The slippiest, claggiest mud in the world. I specced my bike for extra wide mud clearance because of the horrible nasty stuff.