WetAugust is absolutely on the money here as taking issue with Bob Stewart is very definitely not the way to go.
For the record, your ds's name was not mentioned nor was his age or any other identitfying information shown on Bob Stewart's website or, as far as I can ascertain, in those local papers that published an account of the incident,
Under the circumstances, it would seem that only those family/friends who knew that your ds was in this particular unit would make a connection with published accounts of the incident in the, most probably unlikely, event that they happened upon them.
Even if that were to be the case, in the absence of identifying information it's also unlikely that they would necessarily assume that your ds was one of those who absconded from the unit and I therefore very much doubt that you or your ds can have a claim in law for defamation/libel.
Clearly, Bob Stewart is not one of the 'bad guys'. In fact, you have cause to be extremely thankful that the account of the incident he placed on his website has provided you with further ammunition information in support of your contention that your ds should not have been placed in a forensic unit.
You also have cause to be thankful to this MP for having got off his arse tabled questions in the House within such a short time of the incident.
Had he not done so, I very much doubt that the 'external inquiry' referred to in the local press report I have reproduced above would have been commissioned. If he hadn't been on the ball, it's possible that the incident would have escaped Ministerial attention and it may be that wider scrutiny will occur when Bob Stewart's questions are answered.
In short, the Bethlem are now required to publicly account for their failure to protect adolescent patients who are diagnosed as being a danger to themselves as well as to others, and this can only serve to strengthen your/your ds's case against them.
The Bethlem's sloppy deficient practices appear to have extended to the dis information given Bob Stewart who has, no doubt, acted purely on basis of what he was told when he queried the incident.
This begs the question of what hope do you, as the nearest relative of your ds, have of obtaining a truthful account from the Bethlem if a Right Honourable Member of Parliament is told a pack of lies given misleading information by them?
Please don't allow the emotions that have inevitably been stirred by the thought of your ds being placed with dangerous offenders or that you have, virtually accidentally or incidentally, discovered second - or in this case probably eight or ninth - hand information that should have been made available to you at the time of the incident, to lure you into expending valuable energy on a knee-jerk reaction because that plays right into the hands of institutions such as the Bethlem is unlikely to achieve the outcome you want.
First and foremost, your task now is to ensure that your dc is not placed in another forensic adolescent unit and that all authorities/agencies involved in his care do not continue to exclude you from their decision making.
I know this is easier said that done, but please try to resign yourself to the fact that holding the Bethlem to account, together with any other authorities/agencies that were party to placing your ds in the Bill Yule, is not something that will be accomplished in a matter of days, or weeks for that matter.