The desire of some LHR advocates to focus solely on hub transfer business is akin to demanding butter but denying the need to provide bread. The market segments which represent LGW's core business are growing, and demand for them must be met somewhere.
Nobody is denying that Gatwick is a busy airport and would benefit from another runway. The problem is this would do nothing to change the situation at LHR.
The desire to create a hub at LHR will not be affected by allowing more P2P flights form LGW. What would be the case however is that by building a new runway at LHR the likes of BA and Virgin would bring flights back over to LHR thus freeing up capacity ant LGW and providing a possible solution to both problems.
Those who would like to see expansion at LHR are not opposed to the LGW proposals in their own right, we just don't see it as having any bearing on what was supposed to be the original plan. To turn LHR into a major hub airport. Personally I would like to see both happen but know that the politician would never have the cojones to do it.
As for the works on the M25, the section around LHR needs widening now whether the airport is expanded or not. TFL and the taxpayer WILL be paying for this regardless of what happens adjacent to it. When comparing costs only the amount over and above that paid by the taxpayer should be taken into account.