Unfortunately, you can't just attend his talk or at least you have to pay to
attend the full day which is pricey at £88 GBP (£56 for students). I did
contact the tcij about this and they said this was the case. On the other
hand the other talks do look very interesting so it might be interesting to
listen to the other speakers as well.
The link giving the title of his talk is here.
http://www.tcij.org/summer-conference/class-information/#Freedom
For bookings ...
http://www.tcij.org/summer-conference
I will look to go if I can so if any other Trisquel users based in London
intend to go then do let me know. It would be nice to meet up.