Perhaps, the ONS wanted to leave it until the last minute, so as to make things difficult.
I don’t think there’s any doubt. There was a false report (think it was in the Times) a couple of weeks ago that said they were going with sex. Then this announcement at the last minute.
So glad FPFW are reacting so fast. If the ONS (and of course others in the future) think it’s easier to shaft women as we would be less likely to object, then we have do demonstrate loud and clear that massed angry women can object more than a tiny number of hyperbolic transactivists even backed, as they are, by their well-funded institutions such as Stonewall.