This is what the SDP
says.
It is a little vague in parts and does not specifically mention protecting children from being taught they might have the wrong bodies. (The ‘Education’ section mentions replacing PSHE with ‘Wellness’.)
This Sex Based Rights part does seem quite balanced in its approach overall though I think.
SEX-BASED RIGHTS
The liberal pursuit of individual autonomy and desire must be balanced by the common good. Some citizens feel at odds with the physiology and social role associated with their natal sex and can suffer distress. Transgender people should be treated with dignity and respect, in keeping with their acquired gender in most situations. However, these rights must be balanced against the need of natal females for safety and sporting fairness. Biological sex is real and politically significant. This requires an absolute stance on relevant legal definitions in some domains.
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We support segregation by biological sex in sport. Fair competition is not secured if male-bodied transgender athletes are permitted to compete in women's sport and, in the case of contact sports, the risk of injury can increase significantly.
We support segregation by biological sex in prisons and women's refuges in order to safeguard the safety and privacy of natal females. Separate prisons or prison accommodation should be provided for transgender citizens to ensure their safety and privacy.
Transgender individuals wishing to change their sex marker should be allowed to do so. However, we support the continued necessity for medical gatekeeping in any legal change of sex marker. We oppose proposals that would allow someone to change their sex marker by self-identification only.
The Equality Act and Gender Recognition Act will be amended to ensure that sex-based rights which require protection in key domains are not undermined by a change in sex marker:
Healthcare spending and resources for gender dysphoric individuals, including long-term psychological intervention, should be provided at sufficient levels. Physical or drug-based medical treatments for gender dysphoria should be prohibited for anyone under 18 years of age.
We support the retention of biological sex and gender identity as distinct categories in public sector data gathering such as crime statistics, poverty metrics or public health research.
We support the use of plain English for discussions of biological sex in health and reproductive care.
Their whole manifesto is here:
General Election Manifesto