The shares have been priced at between £2.60p and £3.30p but are expected to rise in value when the company floats on the stock market.
The company is currently valued at £3.3 billion but analysts at Panmure Gordon say it could be worth as much as £4.5 billion, the Daily Telegraph reported.
Former home secretary Alan Johnson, who worked as a postman as a teenager, told the newspaper: “There is a vast difference between pricing Royal Mail shares conservatively and undervaluing them by £1 billion. This is ripping off the taxpayer on an epic scale.”
The Government is selling up to 62% of the business, with a 10% stake being handed for free to Royal Mail employees.
But Labour’s Chuka Umunna has urged the Government to pull the plug on the privatisation to prevent a “massive bonanza” for city speculators, despite the late stage.
The shadow business secretary reiterated his concerns that many Royal Mail property assets are in prime locations and could be sold, resulting in a windfall for investors and leave taxpayers short-changed.
The prospectus highlights sites in London at Mount Pleasant and Nine Elms as being “surplus”, with reports saying they are worth between £500 million and £1 billion each, according to Labour.
And Mr Umunna refused to support or condemn potential industrial action by postal workers linked to the controversial sale of the business.
He told Sky News’ Murnaghan there was a huge coalition of opposition to the Government’s plans to sell-off shares in the organisation.
He said: “Now they are pressing on with it, what they need to illustrate is they are going to get the best value for the taxpayer and increasingly what this is looking like is a massive bonanza for city speculators and a huge short-changing of the taxpayer at the same time.”
Mr Umunna added: “It is not too late to pull the plug on this privatisation. Pull the plug on it.
“Tuesday is the deadline by which people can submit applications to get shares. So until you’ve dished out the shares, until you’ve allocated them it is free for the Government to say we have taken a step back and decided we priced this wrongly and decided not to go ahead with it.
“Now I’m saying don’t go ahead with it in principle. But at least if they are going to proceed ensure you get good value for the taxpayer and increasingly we are seeing more and more information coming out which would suggest that the taxpayer will be short-changed.”
It has been revealed that Royal Mail chief executive Moya Greene has written to employees offering them £300 not to take part in industrial action. Workers have been offered a pay increase of 8.6% over three years, including a £300 lump sum in year one if there is no strike.
The Communication Workers Union is asking members to vote on industrial action and the ballot closes later this month.
Asked if it was right for postal workers to take industrial action over the sale and other issues, Mr Umunna said: “I have always said I think striking should be a very last resort and should be avoided at all costs.
“You are not going to have me coming on your programme and supporting strike action.
“But I am not going to condemn our posties either. Let’s not forget these people are absolutely fundamental to our communities. Most people will know the name of their postie.
“These people are not seeking to demonstrate lightly. This is not something people want to do. So I am certainly not going to condemn them but you’re not going to get me supporting huge disruption of services which my constituents and many others around the country get.”
A Department for Business spokesman said: “Royal Mail was clear about its intentions around property in the prospectus.The company disclosed details of its three major surplus sites currently undergoing pre-development work.
“It has also been clear that there are a limited number of other sites with potential for development for alternative use, but for the most part these sites are not readily realisable because they are used by the company’s operations.
“The valuation of the company will be determined through the book building process, and the value of the Royal Mail’s property would be one factor that investors may consider when assessing the value of the Royal Mail.”