SASless
"If you fly at the Minimum Safe Heights prescribed by your OpSpec's using the Obstacle Clearance requirements they require....there should not be a problem to begin with."
Granted - but the heliport the aircraft was diverting to (possibly because of low cloud/bad weather) is obviously on the ground (well on the river actually) - so with the combination of being somewhere you don't exactly expect to be and conditions not being brilliant I could imagine it's not quite that straight forward.
That given - one has to (also) question the grant of building planning permission of a very tall building quite close to a heliport !