I will split my feedback into two:
1. Serena (the host) is a wonderful lady, extremely friendly and willing to help. While my stay at her flat, she provided assistance in terms of city guidance, advice on where to go and what to try, arranged the access to SIM-card coached on activating it; Serena shared with me the brouchures (visitor London guides, maps and others).
2. The flat itself is located in a very heart of London, it has Tesco express and Pret-a-Manger right downstairs, it's very easy to get around the city by walking (i personally did use any transportation means at all for the first two days of stay). The conditions are perfect, the room is not too big, but it has everything necessary and a huge bad. The apartment was very clean, all the devices were working properly.
An overall opinion is wonderful, i enjoyed everything, and it would be a pleasure to meet Serena again.