Hi, Tom, I would agree with the previous postings; I have used the Terminal a number of times travelling in Club and Economy. It is generally great (tho not as good as Virgin's exclusive security arrangements for Business class passengers at T3)
Only two negatives, the security staff let the product down being grumpy and unfriendly, and there is no lounge for Economy passengers. You may think the no lounge thing is no big deal, but all the other terminals at Heathrow and both terminals at Gatwick, Inverness, Edinburgh, Glasgow, etc, all have a lounge for economy passengers willing to pay a fee for entry.
If you are on a connecting flight and have a long lay-over, or you just want to escape the crowds a lounge is useful.... BA just turn you away.