Thanks Dave.
So essentially, without T4, they would be 10mppa short of the capacity that 3 runways would provide (130mppa).
I wonder if an extension to T5 will ever be forthcoming, particularly with BA/Iberia running out of space over there? Could make up for the 10mppa from T4, which will be 40 years old by 2026 and certainly requiring an update one way or another by then...?
Not sure what they would do with the space if T4 was demolished instead of being updated, of course, but sure there's plenty of options!