http://ticckle.com/opinions/2184/what-is-london-s-biggest#

Tourists.

Londoners.

So from the two answers presently in this thread...

Tourists

&

Londoners

Over crowding is our problem. Well then, looks in the vein of there are several interesting methods of management on the table.

As a proud Londoner, I'd say that fact that it's not a 24 hour city like New York. Stuff closes too early even following they relaxed the boozing hours

Glass shiny buildings replacing buildings with character.

London's biggest difficult is house prices

The concentration of those with diverse subcultures and popular ones in struggle with each other trying to corroborate a point (the point is never known)

House prices. I've been to school, lived and worked in London all my life and now I'm being priced out.

The housing market. Investors being permissible to build portfolios and set lovely family houses into loads of tiny, shabby flats. Foreign investors being allowed to obtain lots of flats and then leave them vacant for most of the year (I don't have misgivings with those from other countries buying land here but this sort of behaviour kills communities. It turns new developments into ghost towns). The lack of reasonably priced housing as new flats are built exclusively for the super-rich (look at the development that's happening in Earls Court, on the South Bank and at Centre Point). The continuous destruction of old buildings in order to build generic box buildings for the reason that it's cheaper.

There are lots of Edwardian houses where I live that have turned into shitholes since the landlords don't uphold the properties. They rip out all of the primary features, slap some white paint on and call it a day. The people who owned these houses 20 years ago loved and esteemed their properties and they regularly had front gardens. Then the rolled into town and swept all that away.