There are numerous free online ads for flats in London.
Placing the term ‘Flat in London’ in any major search engine such as Google or Yahoo is bound to reward you with a plethora of results.
You will find a large number of websites adveristing flats for rent and often with pictures of the purported residences. All you have to do is to fill in the criteria of flat you’re looking for and compare the results as well as the prevailing rates. This is usually the more expensive answer to the how to find a flat in London question.
However, it is the most preferable if you’d rather not stress yourself.
Try Gumtree.com, one of the most famous ad website for everything in london or th UK.