Maybe just measure how frequently Amazon drivers leave your valuable deliveries on the doorstep of a busy London street.
Using that as a Stupid Index assumes they care whether your parcels are stolen or not.
Apparently UPS (do they have that in Britain? It's a delivery service, probably the oldest ongoing and the biggest in America) originally required signatures for receipt of deliveries, which meant that if no one was available to sign, they'd leave a note and try to deliver another day. And then after a few failed attempts to deliver, the note would say where you had to go to collect your package.
But they decided -- hopefully based on actual data -- that it was more efficient, even with thefts, to just leave deliveries at the door when no one was there to receive them.
Now you can request deliveries with signature required, and they require signatures to receive booze, but the standard is they just leave it.
Similarly, it can be surmised that credit card fraud is not a serious problem, because credit card companies -- and at least in America, you are generally limited to a $50 loss in the event of credit card fraud, and I think usually they won't hit you even with that -- are very slow to bother to do anything about it: in America, the chip-in-card system that was broadly used in Europe was not adopted for at least ten years after the technology was available and had been thoroughly tested.