Hi Jayne
Welcome to the wonderful illogical world of PRS.
My company promotes and produces concert all over trhe UK, mostly outdoors, for which we have to apply for a range of licenses and also advising the PRS about our concerts.
The easiest comment I would make is that if it is a bona fide venue you are booking they will (and should) have a PRS annual license, so in which case they will pay an agreed annual fee which would have taken into account amount of events held, size of venue V dancefloor.
To show the illogicality of it all, we promote a range of concerts, so this year we will promote Diana Ross and will have to pay 3% of ticket turnover to PRS, yet when I promote classical with a live orchestra it raises to 4.7%! Except if we use out of copyright (over 80yrs) pieces, which then reduces those pieces out of the formula.
So, as you can see quite complex, but I'm sure you're fine if a regular hiring type venue, and if unsure just ask to see their PRS sticker.
Hope this assists.
Mark