Actually, this crab is safe and sound and on display in the National Sea Life Centre in Birmingham. This Japanese spider crab (Macrocheira kaempferi) is the largest ever seen in Britain. It's already got a claw-to-claw spread of 10 feet. and it's still growing.
Of course, all that size doesn't do it much good out of the water, where its weight is such that it can barely support itself. But in the deep it's a nimble, lethal predator.
Thanks for the article, Ida.