From my club's forum:
There's been a spate of attacks on cyclists in Barnes, Putney and near Richmond Park. The little scrotes have been targeting people on bling bikes riding to the park, a guy was pushed off his Venge, they grabbed it and drove off. Seems to be either super early in the morning or later in the evening - just when you're likely to be heading to the park at this time of year.
Also they've been targeting bikes left at cafes - they turn up, grab the bike, shoulder it and ride off.
More info on Twitter:
Same policeman also advised calling 999 ANY time you see 2 men/boys on the same moped in this area regardless of their apparent activities.
There was also an attack in Ham back in April which could be connected.
Usual advice applies about Strava privacy zones, etc. Take care out there.