Fire regs - how do you do a head count in a busy community centre?

Hi! I'm the chair of the trustees of a small but busy village community centre/community cafe and we are trying to work out how to ensure we know how many people are in the building at any given time for fire regs? We have different people leading activities at different times, plus a busy community cafe so does anyone have a workable solution on how to do this please? 

 

I'd be grateful for any possible solutions, even if they are obvious ones as we're scratching our heads here? 

Thank you!