Last entry is at 3pm in winter because it takes a while to queue then catch the shuttle bus etc. and it gets dark, so closes at 5pm.

But if there were actual Police, not just English Heritage security, it sounds like something strange was happening that day, like a VIP visit or something.

It gets so busy that it's recommended to book a timeslot in advance on the website, even if you are a member and don't have to pay.