I received the message below from BA earlier today:
Terminal 5 has new measures in place to improve security and avoid delays. Here is some important information you need to know about using the terminal to ensure you have a relaxing and enjoyable airport experience:
At Terminal 5, you must ensure that you pass through ticket presentation and Security and be ready to fly at least 35 minutes before your flight departs. If you miss this deadline, you will not be allowed onto your flight.