Wait a fucking minute. Stop and read that through properly.
It's factually incorrect to state that 'From its foundation in 1989, Stonewall has produced resources for use in schools aimed at making all educational establishments “LGBTQ+” inclusive.' Stonewall was an LGB organisation until it forcibly, and against the wishes of many people it had formerly represented, added the TQ+ to its remit.
This letter is effectively appears to be requiring the removal of all teaching about anything but straight sexuality from the curriculum. This will set LGB rights back 20 years: we'll be back to a Section 28 situation.
Here's a link to what the Reverend Lynda Rose thinks:
www.christiantoday.com/article/lgbt-lessons-in-schools-the-rev-lynda-rose-on-why-more-christian-parents-need-to-take-a-stand/133452.htm
This is a right-wing Christian movement that will potentially threaten the rights of LGB people. There's no reason for them to mention LGB at all: they could just mention the T. I an extremely suspicious of this. And automatically supporting it will play straight into the hands of critics who say that GC people are in the pocket of the right-wing Christian movement.