T3 easterly extension already has plans drawn up
T2 westerly extension was always envisaged in the original build - the easiest of all the extensions but hasn't happened - this would be a long way from the runways.
T1 re-build (it's half a century old now) inefficient layout, bad design causes airfield / taxiway issues.
Been told by someone who knows but either he was being coy or decisions on timing / sequencing have not been taken yet.
If I was a betting man I would say the T3 extension first but current plans require the closing of what's left of the old Ringway Road as it approaches the eastern end of T3. In order to do that a new distributor road would need to be built from near the Airport Hotel pub to the existing roundabout near the on-site hotels between T1 and T3. It would cut through and remove existing surface car parking as would the additional aircraft apron.
If the management use Cost Benefit Analysis I would reckon this would be a development that works sooner rather than later.
Whatever happens this 9000 space car park provides the breathing space to enable further activity in and around the terminals..