The villain/new guest character is Phil Davis, known to me in his capacity as cab driver from Sherlock and Roman bad guy from Dr who - it is for this reason I think it likely that he is going to be a bad guy in Merlin too, but I don't know for sure. He was part of the entertainers' troupe judging from his clothes.
In terms of main cast there was Bradley (all day) and Colin, Tony, Rupert and Katie, all extremely briefly. I only got pics of Bradley, Colin, Rupert and Tony, and mostly bad ones because they were all of them there and gone in a flash.
Here's hoping for a better day tomorrow!