Hot rumour gleaned from within the NATS/Lulsgate negotiating team.
It is alleged that negotiations are at an advanced level for the approach control function and LARS for both Lulsgate and Filton to be done from exclusively from Lulsgate very shortly after NATS move in down the road.
Ultimately, (I imagine when infrastructure at W. Drayton or Swanwick allows), the plan is to move the function there and include Cardiff.
Only rumour I stress, albeit from a usually credible source, and I have no connection with or detailed knowledge of either unit.