The price of first class stamps will increase from 46p to 60p and second class from 36p to 50p from 30 April.
The postal service has capped supplies before the price rise to 20 per cent of each retailer’s annual allocation in a bid to protect revenue and prevent shops cashing in on higher prices.
Royal Mail spokesman James Eadie said the revenue from the increase was needed to maintain the six-day postal service.
“We do have a sensible allocation in place so that individual retailers can pre-order in advance of the price rise, based on their normal full year expectations of demand,” he said.
“These allocations are in place for all retailers so we can balance the customer demand with the need to protect Royal Mail’s revenues. This is a prudent and appropriate policy. Our priority is to ensure that the proceeds from this much-needed price rise go to sustain the six-day-a-week service which has been loss-making for some time.”
The postal service said it would not comment on reports of individual shops running out of supplies, but said: “What we can confirm is that we always seek to strike the right balance between meeting the demands of our customers and protecting Royal Mail’s revenues immediately in advance of a price rise.”