The panel itself may be sold out but Nerd HQ are streaming it live online via ustream.
The sold out "Conversation" takes place at 6.45pm PDT which is 2.45am in the UK. You can watch it live here: Nerd HQ at Ustream.
The rest of the live streaming Nerd HQ schedule is:
Saturday 7/14 (All times are PDT)
10:00a-11:00a NTSF:SD:SUV (Adult Swim)
11:00a-12:00p Grimm Signing
12:00p-1:00p Tomb Raider
3:00p-4:00p Joss Whedon
4:30p-5:30p Damon Lindelof
6:45p-7:45p Dr. Who
3:00p-4:00p Jared Padalecki