Firstly London University taster courses by no means all full. Take another look if you haven't booked one yet: http://www.london.ac.uk/tasters
UEA have a Maths at University taster day on 4th July - a good day to go as you will find out this Thursday. Apply via: http://www.uea.ac.uk/giftedandtalented/Mathematics+at+University
Cambridge University offering taster days on Saturdays in late June early July in Politics; Psychology; Languages and Linguistics and Maths:
http://www.study.cam.ac.uk/undergraduate/events/masterclasses.html
