Anyone can take it, all it needs is immersion in the Thames (7 times) to cleanse the body, 13 laps around Parliament square to cleanse the spirit and a climb to the top of Highgate Hill to prepare the legs.
I lie.
No previous experience required.
(And Clarion, it would be most EXCELLENT if you were back in some sort of shape, but really there should be more of us in this here London .....)