One small step
Is this enough to wipe out all the profits they've made from this scam, though? If not, all it's done is erode their profit margin a bit: put up their overheads, in effect, so they can just pay up and pocket the rest quite happily.
With so many of these illegal spam calls being anonymous, though, will they even begin to deal with the worst offenders? Time to ban anonymous calls, IMO - at least from non-residential lines - or have a per-call surcharge; even just a pound per anonymous call should wipe out most of these scammers.
Of course, if enough of us blocked anonymous calls, they'd find it self-defeating and have to stop hiding like that anyway...