In spite of the fact that the apartment is small, it has all the comforts you need.
If you are four, you will probably be a little "tight" but nothing unbearable.
I really enjoyed my stay at Ania's apartment since it's a beautiful neighborhood and it's close to every attraction in London( the bus stop is 5 minutes away from the apartment).
Ania is very kind and she has always been available before and during my stay :)