Lancefan
Sometimes it can be advantageous to take aircraft (in your case) from the south 'over the top' of LHR and then join the northern pattern. Especially if we landing on both runways at the same time (before 0700 local), so in this case your AAL98 may be planned to land on the northern runway. In such a scenario it is far better to have arrivals to the northern runway approach from the north, and vice versa, so if an particular aircraft is planned to land on the northern runway, but is in one of the southern stacks (BIG or OCK), it goes 'over the top' rather than having to cross over the other traffic out at 15 miles.
That being said, sometimes it just works out that that course of action is best. If you have a series of Heavy category aircraft inbound from the north stacks, and one Heavy to join in from the south. It might be better to take him over the top and join the back of the stream to the north.
At the end of the day, most of us ATCOs are lazy, so anything we do to lessen our workload is A Good Thing. ^