AFAIK There are four holding areas for flights into LHR
Okham for flights from the west
Bovingdom for flights from the north
Lamborne for flights from the East
Biggin for flights from the South
Chances are you will be held at one of these and then vectored for final.
Not all traffic is held there the other day I flew into LHR
without holding, can't remember the last time that happened.
I believe the are also extra holding areas further form the airport and if traffic is heavy aircraft can be held there before they take the normal hold.