Cliff hadn't been arrested, nor was he arrested. The raid wasn't newsworthy for that reason. They may have Tommy Robinsoned any chance of a fair trial IF it did get to arrest, charge, prosecution.
How? Unless the helicopter footage provided images which could imply he was guilty, I can't see how seeing uniform uniformed personnel going through drawers would influence a potential future jury.
I don't really agree the use of the helicopter that day was justified or proportional, but I don't think it would have affected any subsequent trial of Sir Cliff. The issue for me is entirely whether SYP overstepped their bounds by tipping off the beeb to say "we're off to cliff's, send your crews" (and I think they probably did). If things had turned out differently, and the BBC had ignored the tip off and he'd subsequently been arrested, there would be as many complaints that the beeb was trying to cover his arrest up, so I don't think they can win.