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Again its one of those things that comes down to "maybe".
If you've got all your stuff in a pannier and your bike gets nicked, all your stuff is going too. If you have a rucksack and your bike gets nicked, you might end up keeping your valuables if they grab the bike and do one.
PhilDAS-
Yeah, I get the impression that there's quite a random element here, but snatching of phones from people who are holding them while texting seems more common than actually assaulting someone and demanding their phone. Likewise, nicking the bike + pannier minimises their actual contact with the person and the time they have to hang around. As such, keeping valuables about your person seems like a good move.
Also, it almost seems like having a lock that can quickly immobilise a bike to stop it being ridden away might improve your chances. I know that the Abus wheel locks are sprung-to-open so that there's no chance of them accidentally deploying into your rear wheel while you're moving, but if you could get one that can easily be shut it might be helpful.
ffm
Are these attacks, when they're aimed at cyclists, aimed at nicking bikes, panniers, or both? Is there an argument for switching to a rucksack on the basis that these scrotes seem to adopt a grab-and-run approach, rather than actually tangling with the individual?