I'm not a mathematician by any means, but:
Men: 50% of the population; current male MPs 220/650 = 33.8%
Women: 50% of the population; current female MPs 430/650 = 68.2%
Men are over-represented, women are under-represented.
Transgender: 0.075% of the population
Even if only one transgender person gets elected: 1/650 = 0.15%
So even if one transgender person were elected, there would be twice as many trans people in parliament than is proportional to their numbers in the greater population.
The whole premise upon which the campaign is asking for 50:50 representation would not make sense, because the inclusion of even one transgender person would mess up percentages. (I'm not saying trans people shouldn't be elected, of course, but it puts things in perspective how much we hear about and from this minority).