Postwatch made the complaint on March 18 on behalf of six direct mail companies, which have so far remained anonymous.
The complaint alleged that Royal Mail was abusing its dominant position in the market for delivering letters to favour its own mail consolidation business over its Mailsort service. Mailsort gives a discount to businesses that carry out their own mail sorting for large volumes of mail.
A spokeswoman for Postwatch said that the decision to take the complaint to the OFT was discussed with Postcomm and that it was sent to the OFT because, unlike most other regulators, Postcomm is not a competition authority.
"Our complaint is still valid and is still being taken seriously. We want to see the complaint investigated to bring an action that helps [Royal Mail's] customers," the spokeswoman for Postwatch said.
The issue will now be looked into by Postcomm as part of Royal Mail's licensing conditions, which also includes its pricing policy.
A statement from the OFT said: "Following consultation with Postcomm, the OFT has decided that the industry regulator is in a better position to investigate the matter further. Postcomm has indicated that the conditions of Royal Mail's licence are sufficient to address the concerns raised in Postwatch's complaint (if substantiated), and that it will investigate whether the matters raised in the complaint constitute a breach of Royal Mail's licence."
It said that the OFT may review its position in light of the outcome of Postcomm's investigation if necessary.
The decision is likely to be a disappointment for the direct mail industry because it is believed that Postcomm does not have the powers to regulate Royal Mail adequately and ensure that it is not abusing its position in the market.
A spokesman for WWAV Rapp Collins, which has been pushing for an investigation into Royal Mail, said: "We think this single complaint is the tip of the iceberg, but we believe that the wider problem is Royal Mail's ability to act anti-competitively and abuse its position in the wider marketplace.
"Therefore, we felt the super complaint was enough justification for the OFT to look at how Royal Mail operates in the broader market."
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