I went through T1 a few weeks back for a 17.30 flight, on a Friday Afternoon on a day with horrendous delays (the day of the torrential rain that caused local flooding in London) and I was through within 10-15 minutes with laptop out of bag, shoes off, mandatory groping etc.
All lanes were fully manned in the Domestic entrance. Pretty good and efficient service from the BAA.
I went through the same day, T4 Fast Track, for a 2030 flight, full fare business class ticket.
It took ages to get through, with only one of the two tracks open and the attitude of one of the staff members with a lady in front of me left something to be desired.
This is the trouble with BAA - inconsistency.