No PC? No evidence!
Pace the informative correspondence attatched to your last item on plod/computer interactions, it should be abundantly clear by now that the Met have no intention of taking this to trial. Because if they did intend to go to trial, they now have no audited evidence trail for Mr Greene's PC or hard drive image.
We can therefore safely infer that the only remaining purpose of the SO15 operation is to serve as an intimidatory warning to others.
I'm still puzzled by the red herring of warrants? These are signed by a judge or magistrate on behalf of Her Majesty. And She is the one person who through centuries of hard-fought tradition is prohibited, along with all Her agents, from entering the House of Commons, except by the express invitation of the House.
Logically, any search of Parliament can only take place with the express permission of the Speaker and/or Sergeant-at-arms. Which, luckily for the Met, is exactly what happened.