The place that you are thinking of is the Underwater Studio is Basildon. Steve Warren used to hire it out with his own reef etc. A word of warning though, it is not cheap and without Steve you will probably need to bring reef.
You are far better finding a local private school that hires out their pool or joining a dive club that has a pool night.
The pool that I use in Surrey costs £23 ph which is probably less than 1/3 of the cost in Basildon.
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