Similar experience at Barts as always. I visit this place Regularly (every 2 months for many years) as it not far away from the office. there is usually any queue there in mid morning. It usually takes total of 15 -20 mins waiting including the blood and pee donation. Never used Dean street just in fear of running into my sparring partners from Paddington etc.
They give you a card with a code so you can phone to hear your results.
They test for Gonorrhoea, Chlamydia, herpes, HIV, syphilis, Herpatitis B & C (always been negative on all)
Finding the clinic can be a treasure hunt on your first visit.