TfL had better start building all those extra lines now if they want to
stand a chance of getting them in place by 2016, not to mention John
Prestcott building the houses for the extra people to live in.
Then there is schools, shops, pubs etc etc.

The article suggests an increase in demand for rail and tube and then
goes on to say it is mostly expected to come from trains, so new tube
lines sound unlikely. This would also imply that the increase on the
tube alone is somewhat less than 24% if most of the new capacity
needed is expected to come from rail.