There are currently, according to HMPO approximately 1,300 male sexed transwomen in male prisons. I'm sure they'd like to move to one of the 3,400 female spaces.
Maybe if we release the 1,100 women currently behind bars for council tax evasion, we could have 1 male sexed to 2 female sexed inmates in female prisons.
Google Karen White for the risks posed to women.