For the guest lecturers coming in rather than separate emails or places on the website they should be collated into one place and made into a timetable for ease of access. It is hard to plan guest lectures you want to go to if all the information is separated. There could be sections in the timetable that show the date, lecturer, subject and relevant faculty of each guest lecture.
Visit culturenet.co.uk for all public University events including lectures. There is also a mailing list you can sign-up for with regular updates applicable through the website.