Royal Mail has warned that Ofcom's decision to investigate changes to contract terms for Access customers will create "a period of uncertainty in the UK postal market".

Planned changes to some of Royal Mail’s Access contract terms have been suspended as Ofcom investigates a formal complaint made by rival TNT Post in February.

TNT Post believes that the planned changes breach conditions imposed by the regulator ahead of its privatisation last year.

In a statement yesterday, Royal Mail said it was keen for in the investigation to be concluded as quickly as possible.

“We believe the changes are fair, reasonable and fully within the guidance provided by Ofcom's March 2013 document on end-to-end competition,” the operator said. “We are concerned that Ofcom's decision to investigate under its Competition Act powers may create a period of uncertainty in the UK postal market.

“The suspension of these changes creates a significant asymmetry in the market, as upstream and direct delivery competitors are not constrained in the same way,” it added.

The operator was due to change contracts with 31 Access customers at the end of March, including other mail carriers that Royal Mail provides final-mile delivery services to.

The changes would have seen  the introduction of a price differential for London, urban, suburban and rural areas to help offset costs in areas where delivery is more costly.