Coppi: As per the website.
Don't worry about it - the attitude there seems to be genuinely relaxed. I saw a couple of the managers there, and they were pretty dressed-down. The panel were tidy but not formal. Just be comfortable.
I wore an open-necked longsleeve shirt that didn't need a tie and dark trousers. Neither of the other candidates with me wore a tie - one wore a jacket, the other wore a jumper. Of the group we crossed over with, three quarters wore ties.
Rick: Thanks!