@ Skipness
LHR's rail connection to LGW: Why? What are you basing this on?
A semi-fast rail link from LHR to Guildford (via Staines & Woking) was one of the routes on BAA's Airtrack proposal for pax & staff modal shift from car to train. There is already a train from Reading to LGW via Guildford, however as part of their expansion plans LGW are also calling for improved train services for pax and staff.
The Climate Change Committee reported 60% growth in aviation can be permitted within the Climate Change Act target of an 80% reduction in greenhouse gasses by 2050; though this is subject to government approval.
All I'm suggesting is that a semi-fast train service via Guildford would combine both LHR & LGW requirements. Simple really !