Royal Mail is to raise the cost of a first-class stamp by a record 5p to 46p in April, the company has confirmed.
It will be the largest increase since first-class postage began in 1968. A second-class stamp will rise by 4p, taking it to 36p.
Regulator Postcomm gave permission for the price rises last month.
Royal Mail currently loses 6.4p for each stamped letter it delivers. The price rises should provide it with £380m in additional annual revenues.
There have been larger percentage increases, notably in the high-inflation 1970s, but a 5p rise on a standard first-class stamp would be unprecedented in cash terms.
"No-one likes to pay more and we regret having had to take these tough decisions on pricing," said Royal Mail chief executive Moya Greene as the company unveiled the price rises.
The price rises, which will take effect from 4 April next year, were part of series of proposals outlined by Postcomm.
Postcomm said the changes would help Royal Mail to fund its modernisation programme and help safeguard the one-price-goes-anywhere universal service in the UK.