I had neither kith nor kin in England, and was therefore as free as air -- or as free as an income of eleven shillings and sixpence a day will permit a man to be. Under such circumstances, I naturally gravitated to London, that great cesspool into which all the loungers and idlers of the Empire are irresistibly drained.

What is the difference between lounger and idler here?

Question

I had neither kith nor kin in England, and was therefore as free as air -- or as free as an income of eleven shillings and sixpence a day will permit a man to be. Under such circumstances, I naturally gravitated to London, that great cesspool into which all the loungers and idlers of the Empire are irresistibly drained.

What is the difference between lounger and idler here?

Answer

Hi! They really have the same or a very similar meaning. They both can mean someone who is lazy and prefers to relax and do nothing rather than to work or be productive.

Specifically, 'lounger' means someone who prefers to relax. 
'Idler' means someone who is lazy and does things slowly.