I don't know if this has been posted elsewhere; I didn't find it, so:
4w.pub/the-fall-of-stonewall/
As ever, it's "follow the money":
In the years between 2003 and 2013, Stonewall had gained charitable status and grown to an income of £4,334,054, triple what it had been a decade earlier. Whilst the promotion of "good practice" had long been embedded in Stonewall’s work, it became clear that if the charity were to continue to grow a new cause was needed.
"In the year after the T was added to the LG and B Stonewall’s income rocketed, most notably with a donation of $100,000 from the Arcus Foundation"