You may find my experiences at St Pancras a few years ago are relevant. I took the precaution of emailing them first: So far, so good. But a different story at St Pancras on the day. At first permission to film or photograph in the Station was flatly refused at the Station Manager's office but I persisted, showing the duty manager the correspondence. After much phoning and consulting, he reluctantly agreed, but insisted that I do a "Safety Course" there and then. This took about 1/2 hour and taught me nothing I didn't know already. At the end, I had to sign lots of paperwork wear a badge and vest and leave my monopod with them. Good luck at St. Pancras.