According to this recent article, by James Kirkup in the Spectator on 19th January, the most recent statistics available from the Ministry of Justice show that 18% of the men in prison who aren't trans identified, are currently serving time for sexual offences.
Amongst those who identify as transwomen, the percentage jumps to "between 60 and 61.3%". (That's those who don't have a GR certificate, because statistics covering those with a GRC are harder to separate out from the female prison population and are not yet available).
There are two other statistic we need to make sense of this - what is the population size for TW and, from this, what proportion of TW are sex offenders?