On reflection, realistically there is no chance that they will delay the passengers coming in from the stock broker belt. These long haul passengers will argue that it is ridiculous that their service should suffer due to failings in a local service. And I agree.

Zone 3 rail links should be underground. The wrong sort of clay arguments no longer wash. In any case tunnel under the existing lines to be safe - link up to London Bridge, then onto Charring Cross, Green Park and beyond using the old Jubilee tunnels.
Connect up with East Croydon in the South and this would surely provide an extremely useful and popular service, that would take the pressure off the BR lines/roads into London. Sorted.

And in the meanwhile, sorry, the BR service into London must remain at least at the same level.