more likely redistribution of long haul flights from Heathrow, although that has eased in the short term due to mixed mode useage of Heathrows runways about to start freeing up more slots.
With HST it's more likely that people in the BHX catchment area will be going to LHR than vice versa alas because the starting point is that the variety and the better deals and connectivity in London are suddenly on your doorstep. Incidentally, the removal of the Cranford agreement allowing mixed mode is to be used in times of disruption to get the operation back to normality ASAP in the first instance. I don't believe Geoff Hoon's intention to allow mixed mode in normal operation has been approved by our new green friendly coalition.