In line with British Triathlons new transgender policy which came into effect on 1 January 2023 (see both the policy and implementation guidance here), Tri-Anglia requires three race categories to be offered when entering the relay which are All Open, All Female and Mixed.
The Female category is open to athletes who are the female sex at birth and an Open category open to all other athletes. Therefore, if you have a mix then you enter the mixed category.
This means transgender women who were the male sex at birth will be able to compete in the Open category only. Transgender men who were the female sex at birth - and who have or are transitioning involving hormone therapy treatment - will be able to compete in the Open category provided they have a valid Therapeutic Use Exemption (TUE) for such hormone therapy. These individuals would not be eligible to participate in competitive activities within the Female category.