At this point I have to declare an interest. The leading independent salary survey company CELRE has recently joined the XpertHR Group. So rather than risk being thought of as indulging in special pleading on behalf of the salary survey industry, I will refer you instead to a post this week from US compensation consultant Ann Bares, who blogs at Compensation Force. According to Ann:

"It is important for all parties to recognize that there is a difference between the kind of pay information that employees can access for free on the Internet and the kind of pay information that most employers bank on in reviewing and setting their pay programs and practices.

"Most of the survey data that is used and relied upon by employers reveals - for example - not only the timing and method of data collection, but also the number of companies and employees represented in the data for each position and the organizations who submitted data (along with their demographics in terms of size, location, industry, etc.).

"Most of the survey data used and relied upon by employers typically relies on data collection via an independent and valid source (like a Human Resources department) - not self reporting by the job incumbents themselves."

Her point about self-reporting is certainly worth repeating. There is all the difference in the world between payroll data, run off an employer's system, checked and validated and matched to a standard scale for measuring job roles and functions, on the one hand, and data submitted to a website by a self-selecting group of individuals on the other.

Nevertheless, given that employees don't tend to have access to employer surveys, the new web services may be as good a method as any for web savvy employees to glean information on pay levels in their industry. But such people shouldn't expect their line manager or HR department to give them a pay rise every time they say: "It says on the web that my job is worth £X."