A lot of comment has passed, not just in England and Wales but globally, in what has been referred to as the McNally case (formally known as McNally v R.  EWCA Crim 1051 (27 June 2013)), having had a chance to read the report published on BAILII over a week ago, I believe a lot of it has been wrong, including the initial report that it was a 'trans man', verging on the scare-mongering and that sexually active "stealth" transsexuals or women with a trans history have not all been suddenly criminalised.
In March of this year, Justine McNally was sentenced to three years detention in a young offender institution having pled guilty to six counts of "assault by penetration". She (sic, see below) was given leave to appeal her conviction and sentence.
The facts briefly are that McNally (using a male avatar) and "M" met online and continued to meet across various sites and then telephone conversations for the following three and a half years. On M's 16th birthday they met on a few occasions where she gave oral sex and inserted her fingers. It was also alleged she penetrated M with a dildo but this was denied.
After being confronted she confessed and setting up a chain of events leading to her prosecution.
In the judgement Levinson LJ gets to the main question of whether the acts were consensual under English law.
Most times consent is obvious, the boxer entering the ring of a fully licensed contest, for example. The fighter consents to potential injury and can rely on the defense of consent if he or she injures during the accepted "Queensbury rules" of the bout.
Recent cases have shown that if you agree to the rules before and then change your mind after the bell rings then consent effectively becomes rape. In the Julian Assange case against the Swedish Prosecution Authority where he had "sexual intercourse without a condom when it had been made clear that consent was only forthcoming if a condom was used" and there was no reasonable belief that he would have had his way otherwise.
Also there's another case where the victim believed that he intended and agreed to withdraw before ejaculation and failed to do so. It was found that the CPS was wrong in deciding not to prosecute.
In this case M consented because she believed she was involved with a boy. This alone does not mean an offense has been committed, the fact McNally was found to have professed to the victim that they were male and not female.
Some deceptions, like lying about wealth, are not enough to end consent however some are serious enough and this was found to be one. It does not mean there was no defense just that by pleading guilty she chose not to use one. It is also possible to be convicted over a deception of one's HIV status (something misreported) whether or not there is a deception will be decided from the facts of the case..
Where the appeal did succeed was over the long sentence handed out. The justices decided that a breach of trust only applies where the accused was a professional (teacher, doctor, etc) and substituted the three year custodial for a nine month suspended sentence.
Justine McNally undoubtedly has problems ranging from self harm, sexuality and gender issues (although diminishing, if not diminished), prison was not the answer it is hoped help is given outside.
The facts of the case are very unusual and very rare.
What it means is that if you are trans and get lucky one night you are not being criminalised.