The law is no different in respect of this whether you are in England or Scotland and I will tell you now that I share the same concerns as you but, I don’t make the law, I just regurgitate it.
However your understanding is correct that the person has to have lived in their acquired gender for at least 2 years.
Here it is from the government
which then refers you to the England & Wales government website
Thank you for letting me assist you with your legal question. I am glad that I was able to help.
I am not certain whether that answers the question for you or not, but I am happy to answer any specific points arising from this.
It will be my pleasure to help you again either further with this or any future questions you have