First you need to get diagnosed or at lest go and talk to someone about why you 'need' to change your gender, before thinking your police record will stop you.
I would say they ask you this (they did me when I was being diagnosed by UK NHS doctors) to make sure you are not changing your gender, thinking that will be your police record, gone forever.
You may even find that all the things you did that gave you a police record are linked to 'needing' to change your gender. May sound stupid, but I've read stories about other M2F's who did things in their lives, that were linked to 'needing' to change there gender.
When I look back I've done things in my life and that is why I know it can be linked to gender change.
Hope you get to where you want to be xx