This guest did not have to travel to the City to collect the keys. When he arrived at home in the evening I was already there and I opened the door for him. Earlier in the day I offered to jump on a tube in order to bring him the keys to his airport train terminal so that he did not have to travel at all, but he refused.
The flat is 50m away from the District line tracks, very near the station with trains going slowly by the time the get in front of the flat. So for someone used to countryside life it is somewhat noisy when the tube passes however overall it can be considered a quiet flat for Central London standards as it is completely away from road traffic, buses, proximity to pub/bars etc.