Sex And Gender Confusion

I have always gone along with the idea that if a man wants to be a woman or a woman wants to be a man then that's fine but Professor Robert Winston made a valid point on TV last night that you may be able to change your gender, but you can never change your sex, that is biologically cast while in the womb and you are destined to forever have XY or a XX chromosomes.
The Labour party got its panties in a bunch the other week by saying that only women have a womb but that isn't true, there are plenty of women who for one reason or another have undergone a hysterectomy to have the womb surgically removed so that's false straight away.
At birth, the sex is determined by the midwife by whatever set of genitals is between the legs but you can have them removed, added or even be born with both or none so that isn't a great method to tell definitively male from female.
Another way to tell is to measure testosterone and estrogen but that is not always clear as in the case of the
South-African female runner Caster Semenya who had very high testosterone levels and had to take medication to lower her testosterone levels.
So biologically and genetically speaking, a person’s sex cannot change from birth, but their gender can so terms such as transgender are correct while terms such as sex change are not but as gender is the set of expectations, standards, and characteristics about how men and women are supposed to act in society, then the changing from one to the other is not a problem.
Their are problems, such as toilets or changing rooms but ultimately it is down to the person involved to identify with whatever gender they feel more comfortable with and i am as guilty as anyone for getting the ideas of a persons 'sex' and their 'gender' confused so the language needs to change but so does society to just accept it because the most important aspect is the person beneath the clothes, not the designated sex on the birth certificate.