There are Pros and Cons in relation to planning for an Island airport and also for LHR
Pro
-Massive Capital infrastructure project that would create 100,000 jobs across a 5 year time frame potentially many more in spin off maybe another 250,000
-Opportunity for airport operators to plan in a new airport with minimum staffing requirements to keep costs down. Knock on effect of 40,000 additional jobless in West London is a big issue.
-Opportunity of Govt to focus land around LHR for business / housing
-Remove the log jam of traffic on M25
Con
-Too Bloody far. Businesses all along M3/M4 are not going to want to spend an extra hour or two getting out to the Thames Island no matter how attractive it is. BHX /LGW /LTN and BRS potentially become a viable option.
-Staffing...........If you have a specialised occupation where you can only work in an airport then you will travel out to the Island or go to work at another airport. However the majority of people at LHR have a job not an occupation (not trying to be condescending looking at reality) where then can work elsewhere not in same industry but elsewhere.
LHR is too crowded and takes ages to get to But unfortunately its what you got and without causing major employment and other issues expanding it will be what occurs.