Keeping up with the IT security theme the GRA doesn't even need to be changed for the threat agent to be successful. The original GRA has acted as a trojan horse, whether it was designed that way or not.
It was a largely unnoticed and apparently innocuous legal change which has enabled the definition of women to become diluted by adding men who have been given permission to have the legal fiction status of women through gender reassignment, but more importantly as this has happened alongside
a broadening of terms so that the tight category of adults with gender dysphoria confirmed and treated by healthcare professionals who had taken steps or were in the planning process to transition medically/surgically having already transitioned socially (a group estimated in the low hundreds) has become a large group (estimated in the hundred thousands) of disparate individuals under the transgender umbrella who may have sex or gender dysphoria, or be driven by fetishes or other motivations to believe, pretend to believe or simply say that they are the opposite sex and be at least on the face of it accepted as such
the relaxation of initially rigid medical gatekeeping alongside the introduction of easier processes to enable changes of sex markers in key identity documents (why bother with a GRC altered birth certificate if you already have a drivers licence and passport in your new sex?)
these alongside the general growth of individualistic identity based thinking so that 'I feel x therefore I am x' is now a widely accepted paradigm, so that when individuals present in one of the new transgender identities official reactions are to celebrate and praise the individual regardless of how bizarre that presentation might be (eg Friday Pippa not being taken aside by HR for disciplinary action but instead being feted and asked to write policies, advise the board etc).