Thank you everyone for replying - all suggestions have given me something to work with   Yes @PhilipDAth I really should have mentioned that we're using splash pages here for our guests, ideally I'd like to  use prepaid cards as a method of connection (again uses a splash page) which would be ideal for our not so tech friendly guests, last minute guests and convenient for our reception team to hand out a code to guests attending a one off conference.   I've set up the prepaid cards and it works, its just the students like to try and see if they can join the guest SSID to try and get web access and in the process taking an IP address (student byod is not allowed at present)     In the short term I will look at reducing the dhcp lease time further (thanks @NolanHerring ) to see if that makes a difference and will also see if If I can think of a better may to manage the admin side of using a PSK as this could again free up IP addresses (problem being that the key often seems to get out!) ... View more