Muddled
The flight was completely safe above bkn cloud in very good visibility all the way to elstree (where there were "no holes"), and the divert to redhill, which was clear, was a fine plan that would have presented no difficulty. A careful look at the txt exchange shows that it was useful and positively helpful (the best up to date information, and no distraction of any kind). It became awkward when it appeared that Battersea was "open" - OPEN is a loaded word and can be taken to mean a number of things... like perhaps the wx is ok for example. The only unread msg was saying conditions at Redhill were good and it was useful information - which nearly got through.
The heli was in very good conditions "VMC on top" of broken cloud.
There was no txt distraction during the negotiation to go to Batt - indeed only radio as an 'extra workload' including an unlucky frequency change 7seconds before collision.
I am amazed that obstacles are not lit by high intensity lighting especially in close proximity to aerodromes - yes it might have made the difference
You can't be sure he was in cloud despite it appearing so from some perspectives - and anyway clouds still have visibilty sometimes of several hundred meters - so a suitable light may have been seen especially on a boom which was implausibly far from a tall building (which may have been in sight (probably was))
I saw blue sky nearby, so his local conditions are hard to call.
This pilot was famously WRONGLY blamed before for an accident which turned out sometime later to have been a mechanical failure... so it is completely unacceptable to rule out a malfunction, or some other factor, of some kind in this case.