UK regulators - an idea:
How about making it an offence, punishable with a fine which goes to the call recipient tax-free as expenses for time and distress, to call someone and not give the details of your company when you leave a message, either through an automated caller (which should be banned outright anyway) or by person. I, and I'm guessing a growing number of others will not answer the phone to unrecognised or withheld numbers. If you are a legitimate business with a valid reason to call, you don't with-hold your number, you leave a message stating your company name and the purpose of the call, and you leave a number I can call back which is likely to be included in all calling plans.
Actually, a second idea:
If you call me and actually get through, when I ask you from where you got my number, you should be legally obliged to tell me the source, so I can then trace back to which organisation has ignored my instructions that I do not wish to be contacted by them or their 'carefully selected' 3rd parties and again, they can be punished by a fine, which goes to me. </rant>
Clearly having a caffeine issue, just not sure if it's too much or too little...