NBN Co's chief executive has launched a blistering attack on the telecommunications industry, blaming an "overcompetitive" market and "land grab environment" for the slow speeds experienced by consumers.

Bill Morrow also warned that of the 45 internet retailers "aggressively chasing market share" on the national broadband network today, some will eventually lose money and collapse because their margins are too tight.

"We see examples of a headline price for NBN 'super-fast broadband', but in fact it is a 12 megabit per second [download speed]," Mr Morrow wrote in a seven-page document called "Is nbn to blame with its infamous CVC charge?".

"If a consumer has transitioned from ADSL and [was] getting the national ADSL speed average of 9 Mbps, they will observe hardly any difference on the NBN's access network, yet their expectation was far higher given the well-known cost of a $49 billion super-fast network."