Last couple of years there have been YBOD, Draeger and Classic KISS, as far as I know you only need to be a diver (BSAC OD or PADI OW etc) to go for a try-dive.
The pool they use is only 1.3mtrs deep, more like Closed-Circuit-Snorkelling than diving!
On the plus side- its
free! Which is good, but you need to turn up and book early, they have towels and wetsuits but you might like to take your own.
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Know your PPO2, Pre-breath, Use checklists, Validate cells at 6mtrs, Use pure O2 at or near surface, Use a BOV, Don't dive Solo, Change Slime and Cells as recommended by Manufacturer and RTFM!
Beware Fridge Suck!
www.hugsac.org.uk