Raptor Politics:

raptorpolitics.org.uk/2018/01/24/five-years-of-failure-rspb-withdraws-from-peak-district-bird-of-prey-initiative

raptorpolitics.org.uk/2018/01/23/hen-harriers-peregrine-are-likely-to-disappear-as-a-breeding-species-from-english-red-grouse-moors-within-the-next-decade-or-less

I'm guessing, but it looks to me that the RSPB felt they had to try a soft collaborative approach first; I wouldn't be surprised if they now resort to harder, more expensive legal challenges & ask difficult questions of the police about the prosecution cases that failed. I can't see them dropping it - it's high profile & it's their mandate