LHR - The distance isn't so great, but the congestion more than makes up for it. I expect as routine about 30 mins taxi time for departure and on average that seems to be about right. Arrival... your guess is as good as mine! We arrived late once after an extended flight time, and then discovered that our stand was occupied by a Tech aircraft from another carrier and no alternatives. Sat on brakes and waited with hot bits running hot for 50 mins - total taxi time 70 mins. Stand changed late so no equipment in position as we arrived - further 10 mins.
LHR can break your heart if you let it - An incident as described above or in the OP post will undo all and any good work done in the cabin as customers have to watch their Transport/Meeting/Appointment get buggered up.