Royal Mail has imposed a cap on the number of stamps retailers can as customers stockpile them in advance of the price increases set to hit at the end of the month.

The move is seen as a way for Royal Mail to ensure it profits from the price rises which will increase a first class stamp increase from 46p to 60p on April 30. Second class stamps will rise from 36p to 50p.

Royal Mail has capped supplies before the price rise to 20% of each retailer’s annual allocation.

A Royal Mail spokesman said: “These limits are in place for all retailers so we can balance customer demand with the need to protect Royal Mail’s revenues.”

According to The Daily Telegraph, retailers have experienced a five-fold increase in stamp sales. But Royal Mail is refusing to restock them when they exceed their allocation.

Online supermarket Ocado ran out of stamps earlier this month and grocers Asda, Sainsbury’s and Morrisons are reported a sharp rise in demand.

But health and beauty retailer Superdrug said despite stamp stocks running low it had been told by Royal Mail it would not get any more stamps until April 30. The retailer has appealed to Royal Mail to lift restrictions so it can “help customers save money”.

It has been reported that one customer attempted to buy £5,000 worth in Camden to be told there is a 72 stamp ration per person.

Shadow postal affair minister Ian Murray said he would write to postal regulator Ofcom calling for it to look into Royal Mail’s “shameless profiteering at the public’s expense.

He said: “If it is the case the Royal Mail is rationing the supply of stamps before the price increase that wold seem to go against the spirit of what Ofcom was trying to do with the deregulation of prices.”

Labour chairman of the Commons business, innovation and skills committee Adrian Bailey said: “To restrict the number of stamps retailers can get seems to me to be a restriction of trade.”

Sheets of stamps have even been selling on auction site Ebay, with 100 first class stamps up for grabs for £50, making the seller a £4 profit.