If you think your event is likely to be very popular and oversubscribed, or there are security considerations you should give serious consideration to ticketing the event or having some kind of registration system in place.
There are various options for registering people for your event. You can ask people to register to attend by emailing a particular email address; you can set up a form on the LSE website for registration and download a spreadsheet via cms (speak to the digital team for advice on this); or you could make use of LSE's online store. Registration does have to be handled by your department, as it is not a service the Events Office can provide for events outside the PLP.
For ticketed events organised by the Events Office we have a policy of over-ticketing, as for any free event we expect a significant drop out rate. It is up to you whether you wish to over-ticket. If you do decide to allocate more tickets than you have seats, it is important to make it clear to ticketholders that the event will be overticketed and therefore tickets do not guarantee entry.