I feel like we are covering old ground here, but...
That means that in the fire officers professional opinion you only have enough exits for 780 people.
The legal side of it is this: There is no actual legal stated capacity limit on how many people you can put in your club, it is really your responsiblity to work it out or to get a consultant in to work it our for you. Then this figure can go in your risk assessment, along with how you will control it. This fire officer has saved you the trouble of working it out, but if you don't want to believe him then you work out your own figure and justify your answer.
Now bear in mind that the fire safety order states:
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14. (2) The following requirements must be complied with in respect of premises where necessary in order to safeguard the safety of relevant persons—
(b) in the event of danger, it must be possible for persons to evacuate the premises as quickly and as safely as possible;
(c) the number, distribution and dimensions of emergency routes and exits must be adequate having regard to the use, equipment and dimensions of the premises and the maximum number of persons who may be present there at any one time
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So, to work out the number of people your club can safely evacuate we would look at the current guidance, which I suspect would lead to suggesting that your club only has enough exits for about 780 people. So if you stick 2,000 people in, and we visit you, you will quite possibly end up in court for not complying with article 14(2)(c). We would be turning up to court with our guides and post war building studies to justify our figures.