I can't imagine Westminister hiding it, it would have been whipped out (no puns) during IndyRef surely, as it is a huge smear.
Perhaps the Scottish Government supressed it. Certainly Sturgeon appears to know a bit about it, and she's getting some criticism which I think is unfair (until we know all the facts).
There is always the consideration that it has simply taken this long to get a case together that the PF agreed can go to court.
Timeline and number of accusers will be interesting.
I'm in the "I wouldn't put it past him" camp. He's always been a smug git, even yesterday, and a bit odious for me.