Grounded SLF posted this from the BA website
Going through security
Please allow yourself plenty of time to go through airport security checks.
Please note - if you are travelling from London Heathrow Terminal 5 you must pass through check-in and security at least 35 minutes before your flight departs.
Vagueness 1e - admitted! But the word through is used by BA themselves. Perhaps more clarity is required!
It does seem that I may not be the only pax that thinks T5 is a waste of space. Constraints my ass. The building is big enough to enclose the whole of St. Paul's cathedral!