Not as dangerous as it looks - these two are tethered to the chimney by a piece of blue string

Taken by David Mark from his office window in Balham, London. David said he would get back to us if they fell.

Workers on house roof

Dangerous workers on a roof

In case you didn't spot the blunders David pointed them out: "No tie off on the ladder, both operatives on the roof, thin rope around stack and each man's waist, and potential drop onto glass."