Royal Mail has been given the green light to raise the cost of a first-class stamp by 5p to 46p next April.
This would be the largest increase since first-class postage began in 1968.
A second class stamp could rise by 4p, taking it to 36p, under final proposals from regulator Postcomm.
The move is part of plans for greater commercial freedom for the Post Office under plans to tackle growing competition and maintain the universal postal service.
Royal Mail will decide next month whether to implement a rise of that magnitude. It currently loses 6.4p for each stamped letter it delivers.