Long term plans after TP
The phasing must clearly be:
1 - present TP to modernise and create more capacity on T2 site.
2 - demolish T1 to create space to build new terminal behind T3.
3 - expand new T1/3 parallel to runway 1.
That would create serious terminal capacity that should be sufficient for the foreseeable future even in a constrained LHR/LGW scenario.