Just thought I'd update so those who are thinking of following the Psychiatry UK route have an idea of timescales.
Had the call to book my assessment appointment just now, it's scheduled for the 24th November, so that's roughly 6 months from when the GP sent my referral at the end of May, and about 4 months from when P-UK sent out the self-reporting and informant questionnaires and I returned them mid-July.
Really glad I have a date, as the not knowing when it was going to be was causing me quite a bit of anxiety, although now I will be anxious about the assessment itself!