OK, that sounds like your pre-referral screening for other potential mental health complications. Some portray this as gatekeeping, but I see it more as due diligence.
The psychiatrist will be looking to understand where you are coming from and whether you need any additional support from mental health practitioners. Again, the only advice I can offer is be yourself.

Incidentally, did you know that the Charing Cross GIC in Fulham is part of the same NHS Trust as Broadmoor?