Silver, wow - you've toned down a bit
a. Landspace, which the UK is rapidly running out of. This is mostly new reclaimed land. - At huge cost. Seems they learned a bit from KIx at HKG, but the Japanese kept building them, running up ridiculous debts for totally uncommercial projects.
b. Reduced noise problems - agreed, but how do you factor the cost of noise at LHR, unless govt imposed a specific noise tariff ontop of APD - like ZRH?
c. Cheaper land costs - false, see A
d. Easier planning, with fewer objections - there would still be loads of challenges from environmental groups, not so simple.
e. Easy land connections into Europe, which is easier to serve from the south. - we want an airport for London, not whole of Europe. Limited benefits, as discussed.
f. It is closer to London, and therefore can serve London easier that BHX - and LGW can serve London more easily than either at a fraction of the cost.
Now LGW isn't perfect either - but it is the least bad of all the options.