The vast majority of London commuters live in Greater London, so its housing is largely provided for by itself. Even if you assumed every human being in the "commuter belt" travelled to London daily, the GLA would still account for ~73% of the population, and this is plainly an absurd assumption.
While London may not contribute as much manufacturing, it still manages ~6% of the UK's manufacturing output. At the same time, just retail in London produces almost as much for the economy as rUK manufacturing.
Your whole thesis is laughable. You seem to be upset that the poorer parts of the nation can trade with London to provide it goods and services. Should you not be upset at the farming, storage and transportation rUK "harvests" from abroad? This dwarfs London's "harvesting" of rUK.
London itself has nothing to do with profits from this trade being unequally distributed. Westminster, sure, but London? No.