I found this article very interesting and welcome. In particular, I was relieved to see the open criticism of Stonewall. You are so right, Jonny, that they are taken as the authoritative source on LGBTQ+ issues and many organisations and businesses adopt their policies without question, assuming that they are simply following best practice. It then takes a very brave person to question their employer's policy, knowing that the employer will point to the fact it's Stonewall best practice. Stonewall endorsement also acts as a stifling voice on society - it is very easy to assume that if you consider yourself an LGB Ally, then to take an opposing view to Stonewall must indeed put you on the wrong side of history. A spotlight needs shining on Stonewall's role in all of this.
Jonny, I am due to discuss this with my MP soon as I will take a copy of your article. Sadly, it is a form of armour against accusations of bigotry.