Almost exactly 12 months ago, together with the investigative TV series World in Action, this newspaper commissioned research on the way personal pensions are sold.

One of the ways World in Action chose to illustrate the point that many salespeople are giving poor advice to their clients was to film a "mystery shopper" with a hypothetical problem. A range of insurance company salesmen were then asked to deal with it. In many cases, the advice given was commission- driven and positively dangerous to that fictional person's financial health.

World in Action's "mystery shopper" helped expose some pretty bad practices among salespeople. The usefulness of this approach is apparently gaining new converts: the trade magazine Financial Adviser reports that the Personal Investment Authority (PIA), the financial services watchdog, has held secret trials where "mystery shoppers" ring advisers up and tape the answers given to a fictional problem put to them.

Apparently, independent financial advisers (IFAs) are up in arms about these secret tape-recordings, claiming they are a serious infringement of civil liberties and a serious waste of IFAs' time and money.

As someone who has been both the victim and the author of a few telephone- based pranks in my time, I have some gut sympathy with the IFAs. Yet I can't help feeling that they miss the point.

At present, the main way of checking up on whether an IFA is doing a good job is to have random inspections of their paperwork. This is in addition to tight controls over what the adviser is allowed and not allowed to do at any time. Despite all these checks, there are many cases where the quality of advice given to clients remains extremely poor. In some cases, the adviser is at the very limits of what might reasonably be described as fraudulent activity.

Now that IFAs know their records may be subject to checks, some have become even more adept at verbal flim-flam, their nudges, winks and omissions as significant as any written advice they impart to their clients. The only way to ensure that they are up to scratch is to test them face-to- face. Moreover, to prevent any dispute as to what was said, they should be taped and that tape used in evidence if necessary.

No doubt some advisers will complain that their extremely costly time should not be wasted by fake clients who don't end up as customers. That's fine by me: as a regulator, I would happily shell out a few hundred quid to an adviser that a "mystery shopper" found to be above reproach - as long as they are prepared to pay an equally large penalty if they are not.

Somehow, I have a feeling it's the regulator that would be quids in. In a new story just days after its initial report about "IFA fury over mystery shoppers", Financial Adviser reported this week that in an exercise carried out by Suffolk trading standards department, one third of the 27 IFAs visited by its officers were breaking key PIA rules. Oh dear: time for the hidden tape recorders, methinks.