The law is 1 doorman per 100 people minimum. Thats minimum you may need more
Also if you use a door company that is a limited company they must supply their own insurance (bonus) for themselves
Council run halls have insurance but insist you have your own normally, this saves on them having to pay more next year if they have a claim.
Running an event in one of these type of venues is a nightmare
they even charge you royalties for the music