Royal Mail said the “prudent and appropriate” policy was designed to “protect revenue”.
Reports suggest some retailers are running low on stamps as customers look to buy in bulk before the price rise. The price of a first class stamp will rise from 46 pence to 60p on 30 April. A second-class stamp will go up from 36p to 50p.
The BBC reports that The Royal Mail has capped supplies this month to 20 per cent of a retailer’s annual allocation.
The service said the additional money generated from the price rise was needed to keep the six-day postal service that “has been loss making for some time”.
It said demand for stamps had increased immediately after the announcement of the price rises at the end of last month, but had since dropped back.
“There is a good supply of stamps across the country. We have more than adequate stock in place to meet customer demand,” it said.
Ian Murray, the shadow postal affairs minister, criticised the move in an interview with the Telegraph newspaper. He said he would be writing to Ofcom, asking it to investigate the “shameless profiteering at the public’s expense”.
The announcement of the price rises came after the regulator Ofcom lifted some price controls on Royal Mail.
It claimed the future of the universal service was at “severe risk” without relaxing controls.
The 30 per cent price rise in first-class stamps, and 39 per cent rise for second-class, mark the biggest annual increase in percentage terms since 1975. Ten years ago, a first-class stamp cost 27p, and a second-class cost 19p.
The regulator has capped the price of second-class stamps at 55p. However, this cap can rise at the rate of inflation over the next seven years.