I asked of course for the autographs and I wanted the guy to carry two booklets to Mark, as he just arrived. He went to figure out the situation and came back to me. He told me a thing that I could not understand. In order to get autograph from Mark in British Grove he needs the agreement of his manager?! The guy from the staff went to phone the manager, but nevertheless it turned out that Mark was a bit late in the studio and the staff guy told me there are lots of people involved in this session with Marcus and that the session has just begun. To be honest three more musicians came while I was there for about 20 minutes.
If you are for instance next to BG studios, do not hesitate to ring the door. You won't be kicked out definitely
the guy told me that such situations happen once a month so for them there is no problem to answer and talk to a random guy like me.