The Iron Lady explains it all in her own words.

How I Privatised Britain and Rebooted the "Enterprise Society" is Margaret Thatcher's account of how and why she reduced government control over the economy in Britain (Reason, April 2013). My understanding is that the standard of living increased substantially after her actions. Here are some money quotes.

1. All too often the state is tempted into activities to which it is either ill-suited or which are beyond its capabilities.

   Perhaps the greatest of these temptations is government's desire to concentrate economic power in its own hands. It begins to believe that it knows how to manage business. But let me tell you, it doesn't as we discovered in Britain in the 1970s when nationalisation and prices and incomes policy together deprived management of the ability to manage. 

2. privatisation shrinks the power of the state and free enterprise enlarges the power of the people.

3. to create a genuine market in a state you have to take the state out of the market.