The other is the exemption for medical purposes. It could be claimed that the surgery was essential for mental health so was allowed.
It seems likely that the professional medical backing for surgery came from US based Dr Norman Spack whose treatment of Sudie Gren's child included cross-sex hormones under 16. This is still contrary to UK NICE guidelines and viewed unethical by GIDS
Interview with Susie Green (CEO Mermaids Charity) October 2018:
'My child wouldn’t be here today if she hadn’t gone from Jack to Jackie': Defiant mum whose harrowing story inspired Anna Friel's transgender drama Butterfly praises show - which critics say is just crude propaganda
(extract)
"At her wits’ end, Susie consulted an educational welfare officer and, aged 14, Jackie left school and continued her education three days a week at a special unit for children with long-term health issues.
Meanwhile, Dr Spack prescribed oestrogen, which promoted breast development and helped to stop Jackie growing too tall. (Today she is a little over 6ft.)
‘Her school life in the specialist unit was much less turbulent,’ recalls Susie ‘but she still hated her body.’
So, in a move that many would find extreme, just before Jackie turned 16, Susie consulted plastic surgeon Dr Suporn in Thailand. ‘I asked him when my daughter would be able to have gender reassignment surgery. I expected him to say 18, but to my delight he said she could have it at 16.’
So, supported by psychological reports and a referral letter from Dr Spack, Jackie was admitted for surgery that transformed her life." (continues)
www.msn.com/en-gb/lifestyle/pregnancy-parenting/my-child-wouldn%E2%80%99t-be-here-today-if-she-hadn%E2%80%99t-gone-from-jack-to-jackie-defiant-mum-whose-harrowing-story-inspired-anna-friels-transgender-drama-butterfly-praises-show-which-critics-say-is-just-crude-propaganda/ar-BBOp5c5