One of Britain's oldest institutions, Royal Mail, has lost its 350-year-old monopoly on letter delivery.

As of Sunday , new regulations enable rival companies to offer mailing services to customers regardless of how many items the customer sends. The national postal services regulator, Postcomm, has so far granted long-term licences to 13 operators. The move means that Royal Mail's distinctive red letter boxes could be joined by rival mail boxes in Britain's streets.

Postcomm chief executive Sarah Chambers says that changing 350 years of history takes time. She said Postcomm is convinced that postal customers will benefit from more reliable, innovative and customer-responsive postal services.

But, unlike its new competitors, Royal Mail will continue to enjoy some historical privileges, including exemption from parking restrictions for delivery vehicles and from the value-added tax.