Here are a few resources that might help:
https😕/www.susans.org/forums/index.php/topic,197523.msg1756901.html#msg1756901
http😕/hawaii.edu/hivandaids/Some_Considerations_in_Coming_Out_Trans_to_Your_Parents_and_Family.pdf
one strategy could be to explain your feelings, show some materials and tell them you want to see a good gender therapist...
the gender therapist to help you along, maybe with easy reversible steps first, to help you find out how they make you feel...
so that you have someone to guide you and help you along, and no rash but appropriate steps are made.... appropriate also in your favour, so that it moves along...
Being in the UK you might contact the mermaids, its a group specifically for transgender youth:
http😕/mermaidsuk.org.uk
"We offer information, support, friendship and shared experiences."
They can be contacted via mail...
you could ask there for more information and support.
And this thread migh also be of interest for you:
https😕/www.susans.org/forums/index.php/topic,195129.msg1773970.html#msg1773970
hugs