The postal services regulator, Postcomm, is threatening to undermine universal deliveries through its plans to introduce more competition, according to a Commons committee.

The warning came in the public accounts committee's report on Postcomm's plans to deregulate the postal services market.

Committee chairman Edward Leigh said Postcomm was making decisions "in the dark" and should be cautious about the potential consequences of its plans.

He called on the regulator to demonstrate that opening up the market faster than European regulations require would not damage Consignia's ability to deliver a universal service.

"The postal service that we have always taken for granted is under threat. Soon, most of us may not receive our delivery early in the morning. This retrograde step could well inconvenience people and damage small businesses," said Leigh.

"Overall I cannot escape the fear that Postcomm's approach may well jeopardise the universal service....They simply do not know what impact their approach to increasing competition will have on service. This is decision-making in the dark."

The MPs warned that Postcomm's analysis that competition would develop slowly could turn out to be wrong if firms entering the market chose just to deliver low cost mail, leaving Consignia with the more expensive deliveries.

The committee cautioned: "Increasing competition is a lever for improving efficiency and services, but Postcomm need to demonstrate that rapid market opening would not damage Consignia's ability to deliver the universal service at a uniform tariff."

The report also contained hard words for Consignia, which is losing £1.5 million a day.

It said the loss-making company had failed to meets its own standards of service, and had suffered from a host of serious problems including poor labour relations and inefficiency.

The MPs also questioned Postcomm's plans to open up British markets to European competition before UK companies would have access to their competitors' markets.

The regulator should ensure that the move doesn't "give rise to an uneven playing field and unfair competition", said the committee.

The MPs also warned that the price of stamps may need to rise at least in line with inflation.