I stayed near the Green Park tube station (no not at the Ritz although it's right there) and it turns out that is the staging point for all the Buckingham Palace walking tours. So lots and lots of tour groups mustering there before heading across the park. I even saw one of the tour guides I had spend the winter watching on Youtube!
Anyway, my point is ... I heard one of the tour guides warning her ducklings that pickpockets these days aren't going for wallets, they're going for cellphones. Which seems odd to me but I guess it's because your phone is basically your wallet nowadays.
And I had a nice older Slavic gentleman warn me as I was walking down the street that I shouldn't let my shoulder bag ride too much on my back because it would become a target.