David Cameron said the Royal Mail is at a "massive disadvantage" being owned by the Government and the business would be "set free" by privatisation.
The Prime Minister told BBC London radio:
Royal Mail operates in a competitive market, and right now being owned by the Government is a massive disadvantage. You can't get out there, borrow money, access expertise and capital from the private sector.
Effectively we are setting this business free to be able to do that, to respond to the competition.
The Government outlined its controversial plans to privatise the Royal Mail today - a decision which was widely criticised by the unions.
Every time you lick a stamp you are engaging with a service that's been part of the fabric of Britain for centuries, but that is changing.
The Government will seek to push through the sale of the Royal Mail before unions get the chance to stage a potentially disruptive strike.