The cost of posting a letter will soar next month, with the price of some stamps going up by nearly 40pc.

Both first and second-class stamps will rise by 14p, to 60p and 50p respectively, while the cost of posting large letters will increase from 75p to 90p for first class, and from 58p to 69p for second class.

The price rises, which will kick in on April 30, follow a decision by regulator Ofcom to give Royal Mail the freedom to set its own prices.

'We know how hard it is for households and businesses when our economy is as tough as it is now,' said Royal Mail chief executive Moya Greene.

'No one likes to raise prices in the current economic climate but, regretfully, we have no option.'

The regulator and Royal Mail said the universal service – the notion that posting to any destination in the UK is the same price – would be under threat without the price rise. Royal Mail added that even after the increases, second-class stamps would be the cheapest in Europe and first-class prices would be about average.

But Ann Robinson, director of consumer policy at Uswitch.com, said: 'This increase adds up to a 30pc hike in the cost of a first-class stamp.

'It's an absolute disgrace and another example of the rocketing cost of living.

'Consumers are already feeling worried about their financial situation, with more than half saying they feel less confident about their finances following last week's budget.

'This announcement is only going to dent consumer confidence further – and what makes it worse is that this increase will hit older and vulnerable consumers more.

'While people who can go online will be able to avoid it to an extent, those without internet access will be forced to cough up. It's just another example of the financial penalties facing those who can't go online.'

Michelle Mitchell, charity director-general of Age UK, said: 'While we understand that there is a need for compromise between full price deregulation and ensuring that the postal service remains affordable, Age UK is disappointed that the cap for the second price stamp has been set so high.

'Not all older people have access to the internet and many rely on the post.'

In a bid to cushion the blow, Royal Mail will allow people on pension credit and employment and support allowance or incapacity benefit to take part in a discount Christmas scheme. Towards the end of the year, about five million people will be eligible to buy up to three books of 12 stamps at 2011 prices.