Lovely to read this travelogue, but my heart sank when I read this, as it's an unfortunate reality of living in London at the moment. Thankfully the author was quick enough to evade them.
Be careful about using your phone on the street, day or dark, as it's extremely obvious from far away (eg for somebody sat on a moped pillion) when a potential victim is engrossed in their phone-work and not 100% attending to their surroundings.
Many friends and colleagues have suffered from this scurge, and the moped oiks really have no scruples (one friend was heavily pregnant when she was mugged).
Take care, but don't let that put you off enjoying a great city.