Turin, not strictly true.
The 737s will start to be retired from the start of this year's winter schedule. There is a natural reduction in Gatwick flying during the winter season so the retirements can be accommodated without moving any extra aircraft down.
BA are receiving 10 new A320s (1 already delivered, 9 to go). The intention is that as these are delivered, the rest of the ex-bmi A319s will go down to Gatwick to replace the remaining 737s.
A320 G-MEDK is permanently down at Gatwick as this is a higher MTOW version of the A320 so is able to do the longer flights to Tenerife and Paphos without much of a performance hit compared to the A319s. It also provides extra capacity on busy routes throughout the summer.
The intention is to keep the remaining ex-bmi A320s at Heathrow as they are mostly homogenous with the BA aircraft, along with the mid-haul A321s (which will be converted to ULD loaded).
Champ