All energy suppliers, according to the regulations, are required to display the number of complaints received during the year period leading up to the end of September 2011.
Scottish Power failed to meet the October 31 deadline; the company also suffered the ignominy of having the worst level of customer complaints of all of the so-called "big six" - at a rate of 18.06 complaints for every 1,000 customers.
A spokesman for Ofgem commented on the failure to publish the results.
He said: "We take customer complaints very seriously, as can be seen by the action we have taken against British Gas and npower. Rest assured, we do take action when companies breach the rules and we will be asking for an explanation from any provider that hasn't yet published their customer complaints data."
Responding, having missed the deadline, a spokesman for Scottish Power said: "Scottish Power had informed Ofgem that the company would disclose the annual customer complaint data with our quarterly figures on 11 November."
The spokesman added further: "We will now publish both sets of information on 2 November."
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