Most of the increase is concentrated in London and the South East, already the most densely populatated.
The roads are jammed. London has the slowest journey times of anywhere in Europe.
The trains and underground are jammed with miserable people.
Hospital waiting rooms, schools etc., etc.
House prices are way beyond the reach of all but the most wealthy. Rents are higher in proportion to wages than they have ever been, if you can find a place to rent.
When rainfall is average or below there is not even enough water.